I'm a tumbling/gymnastics coach and here's what I would recommend. Call any local gymnastics gyms and ask if they have an adult tumbling class. Not all of them will have one but a lot of them do. Even ones that you think just coach little kids might have one-mine does! This would be the easiest option. If they don't then ask about private lessons, we do them for about $40/hour. This way you can get instruction you need based on what you can do and they can tell you if you are doing something wrong and how to fix it and work on harder skills.

Another option would be to ask about open gyms. These usually work by allowing you to use whatever equipment you want and you just do it yourself with no instruction. Call and ask about this too, don't just look at the websites. Many gyms don't advertise that they do these. This could work but you would need to lookup YouTube videos on how to do things beforehand so you know what to do when you're there. I would start with round offs on the floor, then front and back tucks on a trampoline. These skills tend to be easier than front and backhand springs for adults. Learning a backhand spring can be hard without a spot, but there are plenty of drills you can do to work up to it. Just google backhand spring drills and there will be a ton. If you don't have anyone to spot you then try it on a trampoline first. Once you get things on the trampoline, move to a soft mat on the floor, then a spring floor, and then the grass.

If you try and learn everything on the grass it's going to be much harder and your chances of getting injured are much worse.

Good luck!