"Right arm is not a valid member of Quest1" Why the error?

The localscript in the TextButton

local Right_Arm = game.Workspace.Quest1["Right Arm"]
local Button = script.Parent
Button.MouseButton1Click:Connect(function()
	wait(0.1)
	workspace.Dummy["Right_Arm"].Position = ("39.4, 3.512, -30.763")
	wait(0.1)
	workspace.Handgun.GripForward = ("-0.002, -0, 1")
	wait(0.1)
	workspace.Handgun.GripPos = ("0, -0.35, -0.1")
	wait(0.1)
	workspace.Handgun.GripRight = ("-0.998, 0.055, -0.002")
	wait(0.1)
	workspace.Handgun.GripUp = ("0.055, 0.998, 0")
end)

It's probably because Right Arm doesn't exist inside the Quest1.

If it does exist, It's probably because it hasn't loaded yet, try local Right_Arm = game.Workspace.Quest1:WaitForChild("Right Arm")

By the way, make sure you check if you added a capital when it's supposed to be lower case.

Also, on this line: workspace.Dummy["Right_Arm"].Position = ("39.4, 3.512, -30.763") Change it to: workspace.Dummy["Right Arm"].Position = ("39.4, 3.512, -30.763")

try doing game.Workspace["Quest1"]:WaitForChild("Right Arm")