Iain Poulson wrote a good article on public speaking.

"But Speaking Is For Experts" This is a common fallacy that needs to be dispelled if you are to get up and start speaking. Conference speakers are not necessarily experts that know more than you. They are just people who have stood up! ... Anyone can do a talk, regardless of your background and skills – you have something to offer.

https://deliciousbrains.com/stop-worrying-love-giving-a-talk/