It is so hard to tell about frostbite in a silkie’s feet with their grey skin. Can you post any pictures of the feet now? Treatment varies. I don’t recommend any treatment if they are outdoors in the coop. But if they can be inside where it is warmer, 2% chlorhexidene, betadine, or Vetericyn can be sprayed or applied daily. Sometimes a warm soak once a day to feet can help. Many times it takes weeks to know exactly how much damage is done.