Was he outside? When it is this bitter cold, it's best to keep them in a coop or shelter if you can, especially out of the wind and to keep their feet off the frozen earth.
How badly did his feet freeze? He will likely have frostbite, but the severity of it depends on what will happen to him. If surface tissues only froze, he may recover with some peeling and discomfort. If the feet truly froze and the deep tissues are dead, the feet will become necrotic and he might die without drastic measures.
I would suggest treating his feet the same way you would with frostbite in people. Don't massage them, and you can do warm (NOT HOT!) water soaks. Don't let his feet freeze again no matter what, or any chances of recovery he has will be greatly reduced. If he develops blisters, you can use a little antibiotic ointment on them.
It will probably be a few days before you can tell how bad the freeze damage was... just observe him carefully and keep a very close eye on his feet.
Best wishes to both of you!!