It’s not about changing who you are, it’s about changing the way you feel about who you are.
I think of it like your ABC’s: acceptance breeds confidence. The first step toward being confident is accepting yourself for who you are–warts and all. That’s not necessarily easy to do; I certainly struggled with it for a few decades! But it is simple. Think of it as binary–you either DO or DON’T accept yourself. If you currently don’t, then the simple solution is to start doing so. (Not necessarily easy to carry out, but a simple concept, right?)
Getting there is a different path for different people, but a trick I’ve used is “mental redecorating,” which I reference here. It’s not about changing who you are–it’s about changing the way you feel about who you are, and the way you deal with other people’s judgments about you.
If you can get yourself in a different mindset re: self-acceptance, that will lead you toward acting with confidence.
And remember: if you’re not doing you, you’re screwing you.