Go to Menus under Appearance

After clicking popup will appear where you can select your template

You can easily assign your Elementor template to the mega menu. Check below

A Mega Menu Badge lets you add a badge to your menu item. Fully editable with Elementor for custom layouts and styles.

From the Icon tab of the Mega Menu settings, you can choose and assign an icon for your Mega Menu.

After appear megamenu popup under the Mega Menu styles tab you can assign menu width and left right position as well

Frontend View of the Mega Menu