You can put antibiotic ointment on it once, gently because it will be painful, but on the comb, it will just blacken and the dead part will fall off. You don't have to treat it, though. With feet, they'd have to be treated differently. Do not use anything with a benzocaine pain reliever! "Caine" pain relievers can be fatal to birds.
Be sure there is no moisture building up in the coop, that you have enough ventilation up high to exhaust moisture from their respiration and poop and check around waterers for wet spots from dripping beaks and rooster wattles.That is usually the cause of frostbite, however, some birds can become frostbitten for other reasons. I incurred this when an elderly rooster with severe arthritis and bad circulation in his legs slept on the floor during near zero winter weather last year. He was unable from his stiffness and the cold to get on the roost that night. His comb and all other birds' in the coop was fine, but his infirmity led to frostbitten toes and weeks of treatment and he did have to be separated from the flock into a warmer environment.
