Static Block is a custom post type that is available on activating Pizzaro Extensions Plugin.
Navigate to King Composer > Composer Settings .
In General Settings tab , make sure static_block is checked.
Navigate to Static Content > Add New and make sure it has a button just below the title with king composer icon and text that reads King Composer.
Give a title as "Megamenu" item.
Add 4 column row for megamenu item.
Click on the Add Element button. It should popup list of elements. Now add Custom Menu widget under Wordpress. The result will look like this.
Click on Publish button.