One of our kids has social anxiety disorder, and she shared this tip once.
When there's something you have to do that's too hard because of your anxiety or shyness, don't do it. Instead, play a character, like you're an actor. The character is a person a whole lot like you, except not very shy. If it helps, you can pattern the character on someone you know so well that you can mimic them and guess accurately what they might say in any given situation. (Our daughter uses me.) You can practice being that character in less stressful situations, so you'll be able to do it in high stress ones.
It's not you who applies for that job, or talks to your teacher about that unfair grade, or sings that solo. It's your character.
I can tell when she's doing it, but her dad and sister cannot. She says it's pretty effective so long as she keeps in practice.