"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)