Garlic is very nice for healthy birds but for getting rid of mites you will want to use it other ways.
If your not sure they are mites post pictures of them.
Most people reccomend the permethrin sprays and poultry dusts, I haven’t used them so I can’t say they are bad but I bet they get rid of them quick and nice. Personally for my flock I have cleaned out my coop thoroughly and then made a homemade mite spray for coops and one homemade mite spray for the flock.
Here’s what I used to rid my flock from mites
For the coop spray
Get a spray bottle that is clean and put in 2 cups of water, 1 cup of cooking oil (I used olive oil), and a tablespoon of safe dish soap and then spray the coop after you completely clean it.
For the bird spray
Get a clean 16 oz spray bottle and put in 20 cloves of peeled and smashed garlic, 45 drops of eucalyptus essential oil, 30 drops of lavender essential oil, 30 drops of peppermint, 2 tablespoons of white vinegar, a handful of lemon balm leaves and then fill 3/4 the way full with water then spray the birds under the wings, on the preening gland, around the vent, and near the keel is the most important places to focus is spraying. And repeat once the next week