Ivermectin does treat some external parasites but not all. You’d have to know what kind of mites they are and it takes the mites biting the chicken to kill them, usually. Here is more information about it:
https://poultrydvm.com/drugs/ivermectin
The easiest thing to do to treat mites is use permethrin dust. I just treated mine for northern fowl mites using the dust method and it worked really well. And it was easy and less of a fight. This is what I used:
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You simply put it in a sock and powder the chicken paying special attention to the vent area, back of the neck and under the wings. Repeat in about 5-7 days. I repeated one more time in another 5-7.
You will also need to remove bedding and nesting material and clean the coop out well after treating the chickens. I used a permethrin spray to spray the corners and crevices of the roosts.