Put an earthworm in there. See if he takes it, don't constantly watch him. Just put it in his tank and leave the room. Check back every hour and if he hasn't eaten it in 4 hours, take it out. Most healthy garters will have trouble refusing an earthworm. Don't add any supplements. Don't cut a big one in half get a medium sized full one that moves a lot. If he eats then he's fine and you can feed him earthworms until he seems completely healed. Then you can try to put him on pinkies. Also remember to keep him warm. Keep his temp at around 80-90 degrees for a sick or injured snake. Add a lot of cool (I mean cool temperature wise, but if you have some stuff that would be effective and looks nice, go for it!) hiding places. Try not to use an under tank heater. Those will make it harder to provide a cool hiding place. Monitor his behavior and keep us updated! Hope this helped!!!