If you have, or can buy, borrow or steal some Ivomec pour on (or similar generic), then a pigeon fancier's trick is to stand the bird in a 10x diluted solution for a few minutes which will then soak into his feet and legs and kill the scaly leg mites. In addition, it gets into his body and also destroys any internal parasites (eg worms) and it spreads in the blood stream and will kill lice and mites.
I use it on my hens for red mite treatment. I put a few drops on the skin, or comb at the top of the head - where the bird doesn't preen, and again it spreads to kill anything crawling about, and any worms. Because your's has scaly leg, I would also put a few drops on each leg.
Because I keep cattle, I always have some Ivomec pour on in stock; but you would probably be able to get it from a pet shop or internet, for use in pigeons. Do not say it's for poultry.