Sevin Dust.... comes in a 1 lb can.. used to be able to get a bigger bag.
Have someone help you... catch and hold. One holds, turns and helps.... one lifts each wing and sprinkles a little under each wing.. (rubs it in a little) then, the holder can turn the chicken a bit, you lift the rear and spinkle and pat around the vent. Then, sprinkle a bit on top of the tail/back, where the tail meets the back. Some say to add a little up by the shoulders, between the wings on the back as well.
One breeder told me she poured Sevin Dust (clearly from the old bigger bag) into a large "bow" type container.. put each chicken in it, wearing gloves.. "splashed" Seven UP UNDER the underside.. of wings, butt, etc... then, let them go... they shake much off.
Clean the coop and change the nesting boxes... clean the roosts.. sprinkle a little Seven Dust on roost, nests, ground (in the dirt or sand), etc.
Repeat treatment in 10 days.
The Feed Store and others also sell POULTRY DUST, it is a two pound can and Permethrin -- you can use that, it's pet friendly and can be used on dogs as well. It's cheaper due to size of the can. I find it a little less effective, so watch for that.
Good luck.