I'm not familiar with iOS however I certain it has the functional equivalent to what's on an Android phone
The rumble apt was crashing on me all the time when I first started with it. They are clearly working on it and it's getting better but software takes time. Meanwhile you can still enjoy access on your phone to 'rumble' through your browser. I like and installed duckduckgo, it works, searches well without manipulation and has good privacy, Google seems only good for monetizing you now but should work also.
Search in your browser for 'rumble.com', create an account, sign in and find ( in duckduckgo it's the 3 dotted pull-down ) the browser selection menu. 'Add Bookmark' to save-backup this page in case you loose the next step. Next 'Add to home (screen)' to create an easy one touch icon shortcut on your phone's home screen. This is what I had to do with GAB when they were being de-platformed and there was no working apt available on Google play store.