don't feel bad. it happened to mine as she was kicking out of the shell. i tried everything to make it right but her bones twisted too and it was no quality of life for her. one is easier to fix than 2. just make sure the chick is on a very soft surface so the hock isn't further damaged until you can splint.
the easiest way to put the tendon back in, according to the poultry orthopedist, is to straighten the leg to the back and gently pinch with your fingers to roll the tendon back to the middle. you can tell if it is out because the hock will look flat in the back when their leg is bent. if the hock is swollen then it probably won't stay in the first time and may need splinted for a few days to let the swelling go down. a chick chair is easy to make and keeps the chick from aggravating the injury. i used pipe cleaners and medical tape to make the splint, wrapping the tape back over itself so it was not sticking to the chicks leg and then wrapping around the leg. also vitamins in the water may help speed recovery.