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:
https://elementor.com/help/how-to-trigger-a-popup-from-a-nav-menu-item/
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.
https://elementor.com/help/how-do-i-create-my-first-popup/
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
https://elementor.com/help/elementors-theme-builder/
Follow the above steps for customizing the "Plants", "Services", "Floral classes" menus.