I know of a company that has a gym and allows people to bring their own trainers. I’d like to know what I would need to do?

It’s a beautiful fitness center (small though) and they have access to the outdoors. Do I need to be my own business to train there? I’d also like to run bootcamps and circuit training classes. What do you need to be a trainer who just pops in to companys and you don’t work for anyone? This is in Northern California by the way.