"Left Arm is not a valid member of Model" Can someone help me?

well im trying to make a one piece game and i have a problem with a script it is not mine script but i please someone help me fix the error my problem is that the output give me an error it says "Left Arm is not a valid member of Model" please help me ill let the script down please and sorry for my grammar im not english at all and im still learning it.

here is the script:

local Player = game.Players.LocalPlayer repeat wait() until Player.Character local Character = Player.Character local Mouse = Player:GetMouse ()

Mouse.KeyDown:connect(function(Key) if Key == "t" then

    Character["Left Arm"].Transparency = 1
    local LeftArm = Instance.new("Part")
    LeftArm.Name = "BusoLeftArm"
    LeftArm.BrickColor = BrickColor.new("Black")
    LeftArm.Material = "SmoothPlastic"
    LeftArm.Refletance = 0.2
    LeftArm.CanCollide = true
    LeftArm.Anchored = false
    LeftArm.Size = Vector3.new (1, 2, 1)
    LeftArm.Parent = Character
    local w = Instance.new ("Weld")
    w.Part0 = Character["LeftArm"]
    w.Part1 = LeftArm
    w.Parent = LeftArm
end

end)

LeftArm is the left arm using R6, and in R15, LeftArm is broken into multiple parts. For this script to work, you'll have to disable R15. You can do this by going to Develop, opening the game tab, opening the settings for the game, clicking Configure Game, and changing Avatar Type Options to "Use R6."

Do this:

local leftArm = game.Players.LocalPlayer.Character["Left Arm"]