How to make this pop-up magnified box go away on the Android app?

If I press too long while scrolling a book this magnified box pops up with two strange 'bookend' icons and I CANNOT figure out how to make it go away again!

It's hugely distracting. Pressing elsewhere on the page simply causes the box to jump there.

Any help?

If I press too long while scrolling a book this magnified box pops up with two strange 'bookend' icons and I CANNOT figure out how to make it go away again!

It's hugely distracting. Pressing elsewhere on the page simply causes the box to jump there.

Any help?