I would clean the area with warm soapy water. Pat dry the wound and surrounding skin, and then put some antibiotic ointment on it (nothing that contains any "caine" ingredients, as those are harmful to poultry on the wound. You could also spray it with Blukote, Vetericyn, or another wound spray. Most importantly, keep the bird isolated from any other chickens until the wound heals, as chickens can be ruthless to those who are wounded.
Watch out for any signs of infection (pus, extreme swelling/redness, a bad smell, black decaying skin, etc.). If you notice any, treatment with an antibiotic like Tylan50, Penicillin, or another strong antibiotic may be needed. But I wouldn't worry too much--chickens have a remarkable ability to heal from gruesome wounds.