STEP 1: How to trigger a Popup from a Nav menu item?

You can have a mega menu type of navigation, using the Popup Elementor feature. Please check the detailed tutorial below:

STEP 2: How to edit the Flowers popup mega menu?

The "Flowers" navigation item leads to a popup named "Flowers - Mega Menu - Home 2". You can locate this template in Dashboard > Templates > Popups.

Click on "Edit with Elementor" to edit the menu, images, button's link, etc.

Another way to quickly access the Flowers' mega menu is to mouse over the "Edit with Elementor" link and click on "Flowers - Mega Menu - Home 2" popup:

Please check these guides for further information:

Guide to Vamtam Elementor Builder

Follow the above steps for customizing the "Plants", "Services", "Floral classes" menus.