Hello and welcome! It is definitely extremely confusing, as every website that I have seen at least has suggested to use Vaseline, hen healer, coconut oil, or another goopy substance to heal frostbite.
My birds get frostbite all the time, so I can confirm that those do not work to help frostbite. In fact, like
@DobieLover said, it makes the frostbite much much worse, as applying any of these substances is basically applying pure moisture, which is one of the factors that causes frostbite.
One time, I used hen healer on one of my rooster's comb and wattles. The next day, they were even more swollen and damaged. If the frostbite starts to get very bad, you can take your chicken inside in a cage- I suggest using puppy training pads. However, if many of your birds get frostbite, you have to pick and choose who to bring inside, unless you have a ton of space. Chickens with yellow tissue damage are ok- however, if the damaged area is bleeding, blistering, or swelling up excessively, that is an excuse to take your chickens inside for a bit.
You can spray the affected areas with Vetericyn or Blu Kote. Another thing about applying Vaseline is that it causes pain to the birds when you rub it onto their face. I truly do not understand why websites spread false "treatments" that don't remotely work. You tried your best and I do not blame you at all for doing what you read!
I would block any vents. Even though you want ventilation in there, if its getting that cold like you said, it is OK to block off airflow. This is what I have learned at least.