I was in a speech coaching program a couple years ago and the thing that helped me was modelling, it's basically like you're acting as someone else but it's so subtle that your brain thinks you're acting like someone else (which makes you not stutter) but to the other person you're talking normally. That + slowing down, blending your words with each other so to not block airflow. It's not easy, surely takes weeks and months of training but it did fix my stutter like around 60-70%