Cut off as much hair as you can around the wound, although the hair is very short on the picture so you might have to skip that step. Clean the would with povidone-iodine or just diluted iodine, some buns’ skin react negatively to chlorhexidine, but it’s often used with rabbits. I don’t know what you can get in Latvia, of course, it varies so much between countries. Hydrogen peroxide is not recommended these days though, because it can delay wound healing.
Dab dry with something very clean, like a fresh compress. Then you can put antibiotic cream on the sore. Fucidine cream can be used, silver sulfadiazine cream can also be used.
If there is an infection your vet might put him on oral antibiotics. Not all antibiotics are safe for rabbits, here is Medirabbit’s list of safe antibiotics: http://www.medirabbit.com/Safe_medication/Antibiotics/Safe_antibiotics.htm
You want the wound to dry up so infection doesn’t spread. He could lose the injured part of his ear, but that’s not a problem for the bunny, it’s just an esthetic thing. It’s very common with ear injuries though, so don’t be alarmed.