How can I make my gun zoom when this button is pressed?

When the button I circled in this link is pressed, I want the gun to zoom in. How do I make this happen with the following script?

local Tool = script.Parent
a = false
cam = nil
wut = Tool.Parent



function onEquipped(mouse2)
    mouse2.KeyDown:connect(onkeyDown)
    mouse = mouse2
end
function onkeyDown(key) 
    if key == "z" then -- I don't want the zoom button to be z.
        if not a then 
            cam = game.Workspace.CurrentCamera:clone()
            cam.Parent = game.Workspace
            game.Workspace.CurrentCamera.CameraSubject = Tool.Zoom
            game.Workspace.CurrentCamera.CameraType = 1
            Tool.Recoil.Value = 5
            Tool.ZoomedIn.Value = true
            Tool.Parent.Humanoid.WalkSpeed = 10
            a = true
        else
            game.Workspace.CurrentCamera.CameraSubject = game.Players.LocalPlayer.Character
            game.Workspace.CurrentCamera:Remove()
            game.Workspace.CurrentCamera = cam
            Tool.ZoomedIn.Value = false
            Tool.Recoil.Value = 10
            Tool.Parent.Humanoid.WalkSpeed = 16
            a = false
        end
    end 
end




script.Parent.Equipped:connect(onEquipped)