Hello There!
As a person who generally plays Chess.com on mobile (sometimes in PC), I find it annoying that there is no option for HyperBullet (30 Sec/10 Sec) in Android. If you are on IOS then you are able to play hyperbullet. However I found sneaky tips which just might be able to help you.
1] Rewind game method: For this you will require a computer. Once you go to the computer you will need to play a 30 Second game. Then you need to switch to mobile and click on that game (or any Hyperbullet game) and henceforth you will see the "Play 30 Sec" button in the right-hand side corner. Click that and you're good to go!
2] Tournaments: You can play in 30 Sec Bullet tournaments through going to the "tournaments" section.