As nasty as it will be...you will need to remove the maggot with a pair of tweezers or similar object. Wrap him in a towel before starting this. Put maggots in alcohol, water, etc. once maggots are removed, bath the area or or you might need to bath him entirely. The area will also need to be soaked in an epsom salt bath for about 10 minutes daily. Apply vetercine spray to wond. Keep him away from other birds u til he start to heal. I had a small rooster who got fly strike and he recovered. That’s was absolutely disgusting, I then had another baby get attacked by another hen and was nearly eaten to death. I was able to save her as well. Peroxide is not supposed to be good for the. Make sure maggots are not in vent area! Good luck!