A search of “gym management software” will bring up more websites than you could ever look at. And without knowing what you really want the software to be able to do, it is hard for me to give a recommendation. I would check out a few and try to sort out what it is you need.
This was a question/related topic a while back.
Membership management, class scheduling, automated recurring payments, booking management, reporting, access monitoring, member retention tools, online and mobile booking?
Check out https://www.glofox.com/gyms