Do you have a coach to spot you and tell you when you're ready to try on the ground? They can be pretty dangerous if you just chuck them, so make sure you're up to it.
Things that can help you when you're ready are leg strength and power exercises, lots of jumps, and then starting from a block or some mats and landing on a soft lower surface and working your way down until you're at ground level.
Doing a back tuck in the ground is very, very different to a trampoline. It is not like a back handspring, where most kids are just about ready to do it on the ground, once it’s mastered on the trampoline.
A back tuck is mainly a strength and power skill, the trampoline does a lot of work for you. On the floor it’s all you.
At the moment while gyms are closed, you can work on building up your leg strength, leg speed and core speed. As well as lots of leg work, do things like V snaps because they help you to be able to quickly tuck over.
But until you are back in the gym with coaches, don’t attempt this skill on the ground on your own. A quick google search will reveal that quite a lot of people have either been paralysed or killed from doing incorrect back tucks on the ground.