I agree that he has frostbite on his comb and wattles, and that it will be painful for him for a few days. Do not rub or massage the frostbitten skin. Do not apply any creams or ointments to it. The aspirin may make him more comfortable. He should be fine eventually, and his comb and wattles...
Pictures would be helpful. Can he raise his head or is it stuck down? Make sure that he is drinking fluids, and electrolytes could help. Is he moving his neck around like he is adjusting his crop? What are you feeding, and does he have poultry grit? Are there other roosters?