Castor oil is an anti-fungal.
Just rub it all over the infected areas. It makes your feet feel great, starts working immediately - each day keep doing it, and each day it will be better and better. I used castor oil that is cold pressed, cold processed - got it from a health food store. I find it is really good for your skin in general, makes all the cracking and dryness get better.
I tried apple-cider vinegar and tea tree oil before - but they smell terrible and can be expensive. Castor oil has like zero smell to it and I think works better. Especially works good after soaking your foot for a while in hot water to open up the pores etc.