I knew a dog with ringworm once. The vet at the time....early 90's...recommended an over-the-counter treatment. It worked.
What was that medication called? *thinking* Oh! Got it, it was Tinactin.
They can call their vet and see if it's still okay for (non-allergic) dogs. The recommendations or ingredients may have changed since the 90's.
But, they might want some for themselves, just in case.
Love All Life; Thank You For Posting! :)