Simply put, if you do something enough times you will have confidence in it.
I remember learning to drive and thinking about how I can make a mistake accidentally crash. But after a year of driving everyday you are now so bored you consider looking at your phone.
No matter how anxious you are you can not stay anxious when you do something 100 times.
Doing something so much you literally can’t care anymore.
Playing an instrument, public speaking, starting a company it’s all the same. Repeatedly do it until it is common place for you.