[oldE]

Know your subject material inside-out and backwards. If you are confident in your knowledge, that is something to build upon to get you started. Toastmasters will help, as you will get practice in a non-threatening setting.
I too was in sales for 25 years, and used to have a 'comfort number' of 10 (thats the number of people I could address before I felt nervous) Since I am semi retired, I put in time at a visitor information center/Tidal Power plant in this area. After a week, I did my first bus tour. By the end of the summer, I was working humor into the talk to keep it interesting for all of us. My big moment was giving the talk to two bus loads at once (they just showed up) Seventy people I'd never met before listening and laughing and learning for about 15 minutes. An absolute ball.
I also discovered if you have enough microphones put in front of you and cameras pointed your way, you can learn to ignore them and continue to enjoy doing your job. (We had a humpback whale get into our headpond and shut down the turbine for a week or so. News folks all over the place.)
You can do this.
Les