if you are nervous in public especially on a platform. I suggest you give more lecture.

"How to overcome tension on stage?" (Your wording sounds like a construction engineering dilemma, as though you were building a bridge.) Assume that your audience wants to hear your speech. They're on your side. If you can talk to any of them before the speech, even just a hello, then that would help - you can then imagine that if you can talk to each person individually, then you can talk to them as a group (they're still the same people). And don't forget to breathe. :)

Trust your intelligence to have more security of yourself. Don´t be afraid. GOOD LUCK !!!!!!

What are you talking about?

do not be looking into people ... let them hear you. Be nice.