If you feel there’s a huge correlation between your stutter and your confidence then it’s time to work on increasing your self worth. Build confidences in other areas of your life so it carries over. Get good at something, be as healthy as possible; build confidence unrelated to speaking situations. It’ll carry over then. I personally think a huge part of it though is getting comfortable when you are stuttering in front of people. It’s just who you are and the more acceptance that forms around that the more confident you’ll be also. It takes time though for sure, finding a good therapist you work well with and exercise help most in my experience.