To remove the second-level drop-down menu or bring the page back to the upper-level submenu, follow these steps:
1. In the Navigation settings menu, grab the hamburger icon on the page you want to relocate and move it into the upper portion of the list so that a line appears inside the upper-level page element:
2. To remove the drop-down menu completely and bring all pages back to the main menu, repeat the step 1 but drop the pages, not inside another page but where a guideline appears:
Your pages will return to the main menu, however, if there's not enough space, they would be automatically moved to the More submenu.