If the foot is going back, I doubt you'll be able to salvage the leg, but please note that I am not a vet. As much as I prefer doing everything I can to save a limb, chicken, etc., I think your best bet is amputate. If you don't, you run the risk of a serious infection with gangrene or something else. If amputated properly and kept clean, etc while healing, the chick can learn to live on the one foot. He/she won't be able to get around fast, so definitely make sure that the coop/run are secure from predators, but the chick should be able to live a normal life. Your local vet may be willing to amputate it properly if you don't think you can.
Good luck!
Good luck!
