My Uber driver was an actor from London. In London he used to play in Shakespeare and Gilbert & Sullivan shows, though he has a bit more trouble here. Apparently he is told that Americans won't understand his English accent. <sigh>
Anyway, he did get a part in a play where he'll need an American accent. I asked him how he will do that, and he has hired a consultant. He said that it is hard to change your own accent because you just don't hear the differences. Have you ever changed your accent? Or read anything about people who have?