At least fake it 'til you make it.
Some people seem to be charismatic without any effort, but you can learn the "pillars of charisma" and command your audience with compelling stories.
In my workshops, I teach people to be clear, concise, and compelling in front of any kind of audience. Bryan Clark, in his article the New York Times, boiled it down to one word - charisma - and he says you can learn it. I agree!
His article starts out listing folks like Oprah Winfrey and Dr. Martin Luther King. But I'd posit that they both had to hone their skills - Oprah in front of small groups on local tv and Dr. King practiced week after week in the pulpit and on the road - before they became household names as communicators who could influence opinion.
And Clark mentions Gandhi who had charisma but who was hardly an electrifying speaker.
You can read Clark's entire article (link above) or I can paraphrase and boil it down to a few crucial points:
1. According to Olivia Fox Carbane, you've got to have presence. I say have a sense of the room, watch them watching you so you can tell when you have their attention and when you don't. Remember to listen in order to be a better communicator.
2. Next Carbane says you have to have power. My version of that is to say that you're the expert...they came to hear you. So don't hem and haw - be a boss on the stage.
3. Lastly, Carbane says a good speaker need warmth. What I teach is that you should break down the barriers that separate you from your audience. Be personal, let people see that you're human and really share their concerns.
Clark finishes by saying you should start with storytelling. That's the foundation of what my workshops are all about. You're the leader, with an expert point of view, and you are sharing that with your listeners. But you can't just lecture at people. Make it personal, relevant, and relatable by couching your message in an understandable story format with a beginning, middle, and an end.
You may be nervous up there on the stage. But if you check all the boxes above and rehearse - voila! Charisma (or something like competence).