Practice meditating/Self-affirmations/self love daily, avoid toxic people in your life if not then fuck what other people think, understand that you're trying to be the best version of yourself every single day, kill your ego. I feel as if we stutter because we don't have enough self love/ patience for ourself and our self-image is mostly based on how others view us. When we block, we usually look at how the other person reacts (mostly negative because they don't know how to react to the situation) and overgeneralize the other person's thought and thinking "this person is probably thinking what's wrong with him? What's taking him forever to speak?", which causes us to block even more because we feel pressure to perform. At this point I think to myself, fuck it, I'm going to take all my time in the world to say whatever I want to say because I what I have to say is important, which usually breaks my block. It's just takes practice and self-awareness to break out of the habit.