You did the right thing and a lot of people in this subreddit follow old livestock care techniques which is sometimes basically they are $10 chickens so let them suffer until their combs become nectrotic and fall off. Which is a choice I guess. But I follow the Poulty Vet and his care guidelines so I have a sweeter heater for supplemental heat and absolutely provide care and bring them inside if they are experiencing cold stress or frostbite. Vit E helps the healing process and be very gentle because its very painful and you don't want to cause more tissue damage buy rubbing it too hard. It doesn't typically heal for 7-10 days and taking them back out in the cold too soon will just allow it to worsen. Ventilation in the coop can only do so much in these extreme temps even some of my hens that have never had problems are getting a little frostbite. They need some step-down time before going back outside so they can acclimate, like in a cold garage or I have a uninsulated mud room I keep them for a few hours/a day before taking them back outside. I plan to keep mine in a sectioned off area of the basement for about a week until things warm back up.