Remember to include all types of experience that relates to the job you seek. When I first put together my resume, I had been a youth sports coach, but hadn’t done any one on one training. However, I had been in the military and that resulted in learning a lot about training and motivation for physical assessments and other duties on the job. The point I wanted to convey with that experience is that I can train someone to do something they have never done before and be successful. Those skills are pretty universal.
In the mean time, see if you can volunteer (as long as you have insurance) as a trainer at a nearby college gym or help out someone in the field you’re interested if they are willing to document what you do, speak for your skills and help you improve.