If OP can’t give him pain relief then it’s not really a fair situation for him. From the description there is more to the injury than just the scalp.
A vet would be best.
Barring proper vet care, sometimes euthanasia is the more humane option.
If you really want to save him, take him to the vet for proper pain relief and antibiotics. Current pain relief recommendations are that chickens need meloxicam which is not available over the counter.
I personally would euthanize him because he is in pain and stuck in a weird and stressful...