How to overcome stage fright
Well, you're not going to like the first thing which is, you have to go out there and perform. First time is, yes, terrifying, but second time is about 60% less terrifying and third time is pretty easy! It really doesn't take long. Once you can see that bad things really don't happen if you make a mistake, the pressure's off.
OK, so there are other ways I can help with this. Make sure that it is an easy gig. That would be an audience full of appreciative people like at Church or a senior living facility etc They are sitting there just wanting you to do well and cheering you along. Try not to head for an audience where there will be a lot of musicians, like an open mic night. Build up to that. The other musicians are not there to be appreciative of you, they are just waiting until it is their turn.
Lastly, practice, practice, practice! Then practice in front of friends and family before the gig. Also, video yourself.
That way, you can see and hear from the audience's perspective. In time, it will be a breeze! Good luck!