Recently a trick started working for me. Earlier when i used to go to shop, i used to think to myself i shouldn’t stutter/block when talking. Nowadays when I’m about to speak, i tell myself i will speak fine without any issue, i completely believe that i will speak nicely, this kind of believe made it a lot easier for me to handle and I’m gaining confidence. And to add, i regularly try to loosen the tension in my body and take deep, slow and comfortable breath from my nose. Properly breathing also helped me get better control