Menus
Menus can be managed under Appearance / Menus. This theme contains two static menu locations – Header Menu and Footer Menu. More info about managing your menus can be found in the WordPress Codex.
Header Mega Menu
To display the submenu of a header menu item as a mega menu, insert “lsvr-megamenu” into the CSS Classes field. This will work only for top level items and only if the menu’s location is set to Header Menu.

2. Make sure CSS Classes option is checked
3. Add “lsvr-megamenu” into CSS Classes field
4. Save the menu