There’s a couple ways to do it. You could remove the code that unregisters the Header Right widget and then reposition the Primary navigation…..This will require making some customizations to your functions.php file along these lines – https://my.studiopress.com/documentation/snippets/navigation-menus/reposition-the-primary-navigation-menu/
You can also add a secondary navigation which will show up on top of the header, and you could then reposition that to appear under the header if you wanted.