Hi Hannah-
Without using custom coding, the best way to change the mobile display without changing the desktop display is to clone your blocks, and then use the responsive utilities to only show one or the either block on the mobile or desktop versions.
First, create a clone of the block you need to edit. Click on Edit Section > Clone:
Then, assign one clone to hide on Desktops and large screens, and one clone to hide on mobile and tablets. Click on Edit Section > Advanced Control > Responsive utilities:
Then, when you switch between mobile and desktop view in the editor, you’ll only change the block that’s showing on that device, without changing the one that shows up on the other.