Smothering them on the chicken legs with vegetable oil smeared on the legs is often recommended.
It will need reapplied every night.
I am sure there are more things that can be used......
There are sprays specifically for treating for them.
Before applying treatment clean the legs and feet.
Soak the legs and feet in warm soapy water and gently scrub with a soft tooth brush, dry and then apply treatment. Vasaline, olive oil, vegetable oil or specific spray are things I have seen recommended.
Soaking their feet and legs will also make trimming nails easier.
Be sure to have something on hand to stop bleeding in case you trim to short and cut into a blood vessel.
Flour, corn starch or a special product from a pet store work well.
You will need to treat every bird and the coop as well.