I need help my hen has a huge black wound under her wing

[Mayen]

This morning I found my favorite hen with a huge gap under her wing it looks and smells really bad it’s covered with hard black tissue and I don’t know what to do it’s my first time keeping chickens and i am very worried please let me know if you have any idea on how to treat it

 

[sourland]

I would guess that you have a large rooster. That sounds like rooster damage. Slather the wound with antibiotic ointment and make sure that flies do not lay eggs in the wound. I would either remove her or the rooster from the flock.