First, I had one with a slipped tendon that I did not treat quickly enough and had to cull, so figuring out the problem quickly is important. Feel around on its hips and legs, see if something feels out of place. Here's what I'd try. Hold its legs in your right had, and its head out straight away from you, with its belly down, your left fingers supporting its chest. So its laying like superman flying away from you. Slowly lower it, until its dangling by its legs. It will instinctively try to upright itself. This is intended to set any joints in the right place if something is out of whack. It can't hurt, if nothing is out of place. Just try it a time or two, slowly, dont stress the bird too much.