To prevent frostbite Vaseline/Bag Balm is used. If the ointment failed to prevent it then I generally clean affected areas with iodine and let them heal on their own. The iodine prevents infection and helps the areas dry up, wither and fall off sooner. If any birds get frostbite then I look at their environment to figure out why they got it in the first place. A clean, vented, dry coop should not allow for frostbite. It still happens on occasion due to factors beyond our control, but it is often caused by conditions that can be remedied.
I hope this helps. Good luck.