Email:
Hi ____,
{sentence about how I know you}. I'm a data science educator and one day I realized that I might have a lot to learn from a personal trainer (beyond the obvious of how to exercise). If you could spare 20 minutes of your time, I'd love to talk to you more about some challenges I think we might have in common such as:
How you remind clients that their goals are attainable
What you do to be more approachable and less intimidating to beginners
Your approach to correcting "bad form" without demotivating clients
Let me know if you'd be interested in chatting and I can send you some available times.