Renpy's default menus are all set up to use a common screen (called "navigation"), which is shared with the main menu, and is included automatically via the "game_menu" (which is used in the achievement screen)
If you want to customize the menu, you'd basically have to copy the contents of the "game_menu" screen (defined in screens.rpy) which itself uses the "navigation" screen (also defined in screens.rpy)
You could also start from scratch with a new, blank screen and just copy the contents of the achievement screen into it
(I'd recommend reading some Renpy tutorials about screen language for guidance here)