It can be caused by a couple of different things so it may be best to get a vet involved to find the right products to use. Basically, it’s wash gently (don’t scrub, don’t actively try to remove scabs) with a gentle soap like Ivory, rinse, dry thoroughly, apply topical product (I use a concoction that my vet makes) and then wrap over the area in a manner that will keep in clean. I am currently going through this with my 4 y.o. and we also have him on antibiotics. If the leg starts to swell definitely call the vet.