It just came naturally I think, at least in my case. When I started liking myself - appearance mainly I mean - I just stopped worrying that much about stuttering, I saw it as a minor issue in my personality. But again, I need to stress that I developed stuttering around the age of 16-17,due to psychological problems I faced at that time, before that age I was speaking fluently without any problem. For people who struggle with that problem since childhood probably just a confidence boost will not be enough.