From new theme version, Theme has been supported Create Mega Menu function.
You can follow these steps bellow to create it for your site:
Step 1: From your admin dashboard, go to Appearance > Menu to create new menu that using for mega menu.
Step 2: After create all menu with the item you want, move to Mega Menu > Add New and build your mega menu layout by WPBakery Page Builder element and Custom Menu element.
Step 3: Select the menu that you create in step 1 for Custom Menu element.
Step 4: After configured Mega Menu layout, go back to Appearance > Menus section to add Mega Menu for menu item of your website if you want it display as mega menu
After done all of step, please check your mega menu on front page.