Bro TRUUUUUUST you just gotta practice on a trampoline or into a pool until its literally impossible to only land on your neck
Then you go on the grass and do the thing where you start with a floppy sideways one handed backsping, and in like 10 minutes you can literally progress to a real back handspring
You will know for SURE you can backflip then, you just need confidence
Then you run up to a round off and COMMIT