I installed the plugin you mentioned, but it does not seem to work with my theme. I do not see an option to implement the second menu that I created. Do you know if there is a solution? Or maybe a different plugin?
go to Appearance/Menus to re-build the menu.
Don’t use “regular” menu. I have created a new menu named “default”, you could re-build it same as “regular” menu. If you don’t set a page/post a menu, the “default” will be this post/page’s menu.