Confidence in Public speaking is all about self confidence.
Yes, you need to know your subject, which you clearly do if you are about to do talk either in a work meeting or at a large event.
The fear is deep routed in acceptance. It's just fear. Way back, if people were ostracised from a community they may have perished. So the fear can be based on this.
We all want to be accepted; praised even. Fear of making a fool out of ourselves, or someone discovering that we are just pretending to be the expert we appear to be, leads to nerves.
But this is just fear: Our own perception of ourselves and worrying unnecessarily about how people will react.
Imagine for instance instead of a room packed full of 500 strangers, only your best friends turn up. You instantly relax and have no problem in delivering whatever is it is with no fear of judgement.
Now imagine those 500 people as friends you just haven't met yet. It's an exciting opportunity to meet them and make new friends.
It's just a matter of perception.
I can help you with that.