While changing my shower head the pipe (shower arm) moved & will not move back even with a lot of force. If it moved so easily the first time why won't it move now? Thank you Sue

Moved as out of the wall or moved sideways?

Is it an extension arm? Mine has a lever on the side that loosens/tightens the arm.

Please respond to Ma0641 question, Thanks.

John

Moved how? In the wall to one side or moved in the threads? Let m,e explain about a typical shower arm and head.
Your shower arm is threaded on both ends. One end screws in to a drop eared ell and the other into a shower head. Simple, right? Not too much to go wrong here. So tell the way it's messed up so we can help. Back to you, Tom