Is it red? Or oozing? Is your cat looking unwell? If it's infected, the cat might need antibiotics, which only can get from a vet. But if not, cats are pretty resilient. We have a semi-feral cat that had a nasty wound on its leg one time, and noticed he was limping, and was worried it was infected, but since we couldn't catch him, we couldn't take him to the vet, and then was quite worried about him, but then his wound healed, and he was fine.
But if your worried it could become infected, and don't want to go to the vet yet, if you want to try and clean it out, I guess you could maybe try and gently try and wash it with saline or first aid disinfectant like alcohol wipes or iodine wipes. But if you do that with anything that stings like rubbing alcohol or iodine, probably would want to be very careful... may want to put on some long covered gardening gloves.