I learned a technique called 'soft touch' or something like that. It's like really softly touching your lips when saying the letter you want to say. I'm sure there are video's about it on yt. That really helps me. But remember that technique alone Will only help temporarily. It's the mindset that helps te most. Get used to uncomfortabele situations. Go out and order something. Ask a stranger on the Street a Question. That 'trains' your brain to be more and more unsensitive to blocking and stuttering in General which means your miscles Will relax more and the words Will Come out easier