I use a permethrin dust for lice.
Dust then check again in 7-10 days to see if eggs have hatched into live lice...tho the oil on eggs might do the trick.
I check them at night, easier to catch, get them off the roost and use a head light while parting feathers down to skin around vent, head/neck...
Ditto Dat^^^
The lice eggs on the base of feathers are hard to get off....
....best to treat for the lice every 10 days until they are gone and let the chicken preen off the lice egg remains.