Flash brights at them, as you would do with anyone else. I drive a lifted 4x4 and through honest oversight failed to re-adjust headlights after the lift.

Just took a few people flashing brights at me to make me realize and do the (very easy) adjustment to proper specs.

Doesn’t solve people behind you, but it’s not like they’re going to pull over and adjust anyway. Flash brights and consider it a favor to the person in front of the offender.

Telling people they're doing something annoying / dangerous / etc is surprisingly effective. Ask the person smoking next to you to move downwind. Ask the neighbor next door to turn down the TV. Ask the tourist in public transport to move their suitcase so it doesn't block the door. Works every time, most of the time.