That’s a hard one. Do you know anyone who knows them in real life, who could maybe speak to them face to face and tell them they are making mistakes? Lots of mistakes, publicly?
Beyond that, I think the only thing you can do is keep correcting their mistakes. Tag in other competent identifiers to help, because if the errant IDer sees that more than one IDer disagrees with their ID, maybe they’ll stop.
Good luck!