I second LBJ. The hair loss is a consequence of the mites. Both hair and rather big dandruff-like flakes will come off as the mites die. If the skin looks irritated you can put on a tiny bit of Vaseline.
For really bad cases of mites, up to 4 injections of ivermectin can be needed. There are still mites in your rabbits environment, to prevent them from reinfesting your bun, treatment is pretty long. But improvement is often seen remarkably quickly, Ivermectin is a very good antiparasitic.
You can help your bun by brushing him with a soft brush, but do it in the bathroom or even outside if you have a balcony or porch so you don’t get surviving mites whirling about in the house. They can survive pretty long in the environment, especially if it’s moist.
Toys can be put in the freezer for 48 hours (in sealed plastic bags of course), all washable fabrics should be machine-washed. My Bam had mites once 6 years ago, he had two rounds of treatment, he’s been mite-free since.