If you installed and activate UberMenu plugin, then all what you have to do in order to integrate it with Mesopotamia is to navigate to Appearance->Mesopotamia->Header and check the “Enable UberMenu” checkbox then click on “Save All Changes” button, that is all!
In order to assign a menu to UberMenu just assign the menu to the “Primary” theme location from Appearance->Menus->Manage Locations admin page.
Please notice that UberMenu will replace the entire navbar not just the menu.
For more info about UberMenu please check the UberMenu knowledgebase.