By selecting the Appearance > Menus option from the WordPress admin sidebar, you can set the top navigation by creating a menu, and on the left under Theme Locations set the Main Menu dropdown to be your newly created menu and then click save. This will allocate your created menu to the header navigation of the theme.
You also can assign a menu or edit menus using Theme Customizer. Same as logo. The options are under main panels. Appearance > Customizer > Menus > Choose to edit menus or assign a menu.
This theme support 2 depth level of sub menu.