How do u do an if then based on orientation?

Actually they'd work if you wrote them correctly, here, I'll show you what you did wrong.

if script.Parent.Part.Orientation == script.Parent.Part.Orientation(0,-180,0) then

Should Be:

if script.Parent.Part.Orientation == Vector3.new(0,-180,0) then

AND

else if script.Parent.Part.Orientation == Vector3(0,-90,0) then

Should Be:

else if script.Parent.Part.Orientation == Vector3.new(0,-90,0) then

And the last one is perfectly fine.