How can I make this script follow the left arm too, not just the right?

How can I make this script follow the left arm too, not just the right?

This is in a local script inside a tool

-- Variables for services
local render = game:GetService("RunService").RenderStepped
local contextActionService = game:GetService("ContextActionService")
local userInputService = game:GetService("UserInputService")

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local Tool = script.Parent

-- Variables for Module Scripts
local screenSpace = require(Tool:WaitForChild("ScreenSpace"))

local connection

local neck, shoulder, oldNeckC0, oldShoulderC0

local mobileShouldTrack = true

-- Thourough check to see if a character is sitting
local function amISitting(character)
    local t = character.Torso
    for _, part in pairs(t:GetConnectedParts(true)) do
        if part:IsA("Seat") or part:IsA("VehicleSeat") then
            return true
        end
    end
end

-- Function to call on renderstepped. Orients the character so it is facing towards
-- the player mouse's position in world space. If character is sitting then the torso
-- should not track
local function frame(mousePosition)
    -- Special mobile consideration. We don't want to track if the user was touching a ui
    -- element such as the movement controls. Just return out of function if so to make sure
    -- character doesn't track
    if not mobileShouldTrack then return end

    -- Make sure character isn't swiming. If the character is swimming the following code will
    -- not work well; the character will not swim correctly. Besides, who shoots underwater?
    if player.Character.Humanoid:GetState() ~= Enum.HumanoidStateType.Swimming then
        local torso = player.Character.Torso
        local head = player.Character.Head

        local toMouse = (mousePosition - head.Position).unit
        local angle = math.acos(toMouse:Dot(Vector3.new(0,1,0)))

        local neckAngle = angle

        -- Limit how much the head can tilt down. Too far and the head looks unnatural
        if math.deg(neckAngle) > 110 then
            neckAngle = math.rad(110)
        end
        neck.C0 = CFrame.new(0,1,0) * CFrame.Angles(math.pi - neckAngle,math.pi,0)

        -- Calculate horizontal rotation
        local arm = player.Character:FindFirstChild("Right Arm")
        local fromArmPos = torso.Position + torso.CFrame:vectorToWorldSpace(Vector3.new(
            torso.Size.X/2 + arm.Size.X/2, torso.Size.Y/2 - arm.Size.Z/2, 0))
        local toMouseArm = ((mousePosition - fromArmPos) * Vector3.new(1,0,1)).unit
        local look = (torso.CFrame.lookVector * Vector3.new(1,0,1)).unit
        local lateralAngle = math.acos(toMouseArm:Dot(look))        

        -- Check for rogue math
        if tostring(lateralAngle) == "-1.#IND" then
            lateralAngle = 0
        end     

        -- Handle case where character is sitting down
        if player.Character.Humanoid:GetState() == Enum.HumanoidStateType.Seated then           

            local cross = torso.CFrame.lookVector:Cross(toMouseArm)
            if lateralAngle > math.pi/2 then
                lateralAngle = math.pi/2
            end
            if cross.Y < 0 then
                lateralAngle = -lateralAngle
            end
        end 

        -- Turn shoulder to point to mouse
        shoulder.C0 = CFrame.new(1,0.5,0) * CFrame.Angles(math.pi/2 - angle,math.pi/2 + lateralAngle,0) 

        -- If not sitting then aim torso laterally towards mouse
        if not amISitting(player.Character) then
            torso.CFrame = CFrame.new(torso.Position, torso.Position + (Vector3.new(
                mousePosition.X, torso.Position.Y, mousePosition.Z)-torso.Position).unit)
        end 
    end
end

-- Function to bind to render stepped if player is on PC
local function pcFrame()
    frame(mouse.Hit.p)
end

-- Function to bind to touch moved if player is on mobile
local function mobileFrame(touch, processed)
    -- Check to see if the touch was on a UI element. If so, we don't want to update anything
    if not processed then
        -- Calculate touch position in world space. Uses Stravant's ScreenSpace Module script
        -- to create a ray from the camera.
        local test = screenSpace.ScreenToWorld(touch.Position.X, touch.Position.Y, 1)
        local nearPos = game.Workspace.CurrentCamera.CoordinateFrame:vectorToWorldSpace(screenSpace.ScreenToWorld(touch.Position.X, touch.Position.Y, 1))
        nearPos = game.Workspace.CurrentCamera.CoordinateFrame.p - nearPos
        local farPos = screenSpace.ScreenToWorld(touch.Position.X, touch.Position.Y,50) 
        farPos = game.Workspace.CurrentCamera.CoordinateFrame:vectorToWorldSpace(farPos) * -1
        if farPos.magnitude > 900 then
            farPos = farPos.unit * 900
        end
        local ray = Ray.new(nearPos, farPos)
        local part, pos = game.Workspace:FindPartOnRay(ray, player.Character)

        -- if a position was found on the ray then update the character's rotation
        if pos then
            frame(pos)
        end
    end
end

local function OnActivated()
    local myModel = player.Character
    if Tool.Enabled and myModel and myModel:FindFirstChild('Humanoid') and myModel.Humanoid.Health > 0 then
        Tool.Enabled = false
        game.ReplicatedStorage.ROBLOX_RocketFireEvent:FireServer(mouse.Hit.p)
        wait(2)

        Tool.Enabled = true
    end
end

local oldIcon = nil
-- Function to bind to equip event
local function equip()
    local torso = player.Character.Torso

    -- Setup joint variables
    neck = torso.Neck   
    oldNeckC0 = neck.C0
    shoulder = torso:FindFirstChild("Right Shoulder")
    oldShoulderC0 = shoulder.C0

    -- Remember old mouse icon and update current
    oldIcon = mouse.Icon
    mouse.Icon = "http://www.roblox.com/asset/?id=79658449"

    -- Bind TouchMoved event if on mobile. Otherwise connect to renderstepped
    if userInputService.TouchEnabled then
        connection = userInputService.TouchMoved:connect(mobileFrame)
    else
        connection = render:connect(pcFrame)
    end

    -- Bind TouchStarted and TouchEnded. Used to determine if character should rotate
    -- during touch input
    userInputService.TouchStarted:connect(function(touch, processed)
        mobileShouldTrack = not processed
    end)    
    userInputService.TouchEnded:connect(function(touch, processed)
        mobileShouldTrack = false
    end)

    -- If game uses filtering enabled then need to update server while tool is
    -- held by character.
    if workspace.FilteringEnabled then
        while connection and connection.Connected do
            wait()
            game.ReplicatedStorage.ROBLOX_RocketUpdateEvent:FireServer(neck.C0, shoulder.C0)
        end
    end
end

-- Function to bind to Unequip event
local function unequip()
    if connection then connection:disconnect() end

    mouse.Icon = oldIcon

    neck.C0 = oldNeckC0
    shoulder.C0 = oldShoulderC0
end

-- Bind tool events
Tool.Equipped:connect(equip)
Tool.Unequipped:connect(unequip)
Tool.Activated:connect(OnActivated)