What exactly are you trying to do here? Why are you trying to destroy the object that you are tweeting after completing it? Plus, since :Destroy passes self as the first parameter (hence the “:”), you would need to pass that as the first parameter. So if you wanted to destroy the instance you are tweening (assuming it is an instance) after it is done, here is what it would look like:
Tween.Completed:Connect(function()
Tween:Destroy()
— or Instance:Destroy() if you have the instance readily available.
end)