I think that's something we are all working one. I would recommend learning about stoicism. It really explores the idea that other people opinions of you should not affect you. I would say start with the daily stoic and then move onto modern introductory books, and finally stoic philosopher like Marcus Aurelius if you really into it. Although stoicism is good to a point exposure is really the best solution in my experience. You can force yourself to do something logically but you will be uncomfortable and awkward but after continuous exposure that fear will fade and it will feel a little bit more natural. In my experience people forget that I stutter, like friends I see semi often. You are the side characters in everyone play and once you can internalize that you will be ahead of 99% of people even if you do stutter.