You don’t have to be an expert to teach someone else, you just need to know a little more than they do.
Years ago when I became an assistant scuba instructor, I was able to provide huge value to new students despite my having far less diving experience than all of the other instructors. Simply being able to help them out when I could and knowing the process meant a great deal. On the plus side I learned a lot from the questions they would ask, such that it made me a much better assistant (and eventually full) instructor.
For the same reason I started teaching AST-BBST, I wanted to learn more about the material. I probably wasn’t the best student (frankly I don’t know how well I did in the classes other than passing it) but I loved the information so much I wanted to get more exposure to it. Over time as I interacted with hundreds of students and dozens of instructors I feel like I’ve become exposed to more ideas and absorbed more information than I would have without it. I’m no expert but I’m probably better than most.
All of this is to say the Association for Software Testing is always looking for instructors to help teach classes. The class itself is free (once you’ve successfully completed one AST-BBST class you qualify) but the lessons you learn are incredibly valuable.