What an honor to be asked to speak of your experience! You must have a lot of worthwhile things to say to people who are looking for hope and inspiration. That's where I think you start. Try to remember how you felt when you were in their shoes and speak from the heart.
That said, I absolutely hate public speaking and create all sorts of anxiety for myself when forced to do it! Or at least I used to, haven't done it in while.
You have something of value to share, and yur audience wants to hear it. Good luck!!