Add a Submenu from Another Submenu in a Custom Theme

It seems that you are adding the menu levels as separate menus:

  • A “Primary menu” containing the items: “HOME”, “DPRK TOURS”, “INTERNATIONAL”, … etc.
  • A “Secondary menu” containing the items: “INTERNATIONAL GROUP TOURS”, “VOLUNTEER PROGRAMS”, … etc.

However, most themes support at most two such menu-levels, and some even support only one. So, if you are looking to set up a “Tertiary menu” (with items “Group Tours”, “DPRK Add-Ons”, … etc.), I doubt that your theme natively supports this!

Instead, you should consider using just a single (“Primary”) menu, containing a multi-level structure (with even three or more levels). The WordPress built-in menu-editor allows you to edit this multi-level menu using a simple drag-and-drop interface.