I don't know what you're stuck on, but if you're having trouble with this method you could try this other guide I've found:
(1/2) https://www.reddit.com/r/mangago/comments/pdflgv/script_for_backing_up_reading_lists_v10_release/
(2/2) https://www.reddit.com/r/mangago/comments/pg18eg/update_for_script_on_backing_up_lists_v121_now/
In any case you need a computer though
still no bookmarks :(

Is there a way to export or download our want to read/reading/read lists? Mine are really full and screenshotting all of them seems like a huge pain...