I'm so sorry you experienced this OP.
One of my exes had a similar experience with a chiropractor. Not even with genitals, but saying he needed to work on her chest, which she found odd. But she got along well with him and told herself she was being paranoid, so she didn't report it.
Years later, she got a call from the police. Apparently he'd assaulted 30+ female clients, including young girls. The assaults were more subtle with the older women, worse with the young girls who I guess he knew wouldn't be as clued up. He ran a big, popular practice with hundreds of 5* reviews. He tried to flee the country but was found, and now he's now in prison.
If my ex had reported it, she may have prevented him doing these things to young girls. And if someone else had reported him sooner, it might have prevented him doing it to my ex.
I've never been to an osteopath, but I do get a lot of tattoos, which is obviously all intimate, body to body contact, in the zone type stuff, for hours on end, and you get quite comfortable with each other. Yet every artist I've had has been very aware when inappropriate body parts are touching, and they always apologise and slightly shift away, as you would expect. So I just can't imagine him not being aware.
If it were me, I would reach out to whatever the professional body is for osteopaths and seek advice. Just tell them what you've told us and go from there.