Hello,
Thank you very much for choosing our theme and for contacting us.
As I understand we are talking about the main menu http://prntscr.com/mmr3pc if so,
Each submenu for the menu item is HTML template created by means of WP Bakery page builder element Extra menu list https://xtemos.com/docs/woodmart/html-blocks-2/
So, first of all, create the block for each menu item.
As soon as you have all blocks ready, navigate to Appearance > Menu, choose your category menu and add HTML title as shown here: https://xtemos.com/docs/woodmart/html-blocks-2/#mega_menu
If you mean another menu, please specify which one.
Best Regards