Build off of what you are already doing. From your profile I see you teach bootcamps. Offer your current clients a referrel card for classes depending on how many people they get to sign up for your bootcamp.
If you want to do personal training, let your bootcampers know you have times open in your schedule for one on one training.
I agree with Jason, get into a gym as an “employee” an gain experience.
There is no need to have a huge overhead as a new trainer, use your local gyms, parks, or start a home training business, once you get busier and more confident, you can then possibly open your own space, but without a clientele, it’s a risk.