This is from another site from the internet-swelling sounds like possible infection.
If any chickens show signs of lameness or severe frostbite of the comb or wattles, they need to be removed from the flock and treated promptly. Soak the limbs (feet, toes and legs) in room temperature epsom salt water to gradually warm the frostbitten areas. This may take as long as a half hour of soaking. Dry thoroughly and rub bag balm or other salves on those areas. Place the bird in a carrier with bedding, food and electrolytes along with fresh water, in a warm area with no drafts. Check frequently to make certain the chicken is alert, eating and drinking normally. Examine the frostbite areas for any bleeding or infection. If there is bleeding, apply
Blu Kote to prevent pecking, especially if you are treating more than one at a time.
An application of Vetericyn will help prevent infection.