I use the 4-7-8 box breathing technique to active the parasympathetic nervous system, which calms me down instantly. Look it up on YouTube. I also read aloud slowly every day for 15-30 minutes to exercise the vocal folds and puts my brain into a smoother speech pattern. I still stutter but a lot less. 👍🏼 BTW, keep your brain hydrated and try and do daily exercise such as walking, jogging, cycling etc… improves oxygen to your brain.