I used to be like that. Took me 40 years to learn that you can instantly turn into an extrovert and behave like one if you just start focusing intently on your surroundings and on the people you are interacting with and completely ignoring your own thoughts about yourself.
I keep telling people this when they have social anxiety like I used to have and it would instantly solve all their problems with this.
But nobody listens. Oh well...guess thats their problem not mine. I am only throwing the literal solution right in their face.