Your doctor can sell you a bottle of Epi-otic, which is specially
formulated to clean ears of dogs and cats.

When our Basho developed an ear infection, we had to clean his hear once
a day, then apply medication. We wrapped Basho in a towel (for our
safety), then doused a piece of cotton with the cleaning solution, put
it in his ear and rubbed it around, cleaning as much as we could. Have
your vet show you how.