I'm very sorry. I still don't understand question.
You want load module"calendar" in to your megamenu?
you can reference view this links:
www.joomlaux.com/document/jux_megamenu/
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How to load different types of modules into your menu items
In this section we are going to show you how to load different types of modules as menu items. Basically you can load any type of module:
Regular Joomla! modules: login module, quick contact module, external content feeds… generally all modules you have installed on your site.
Custom HTML: embedded videos, external content, community links…
You can also load unique module positions you have set for your modules – position that are not defined in your template.
Loading regular modules
In this example, we’re going to show you how to load the default Joomla! Login module as a Menu Item. Please create a new Menu Item and do the following steps:
*Please note that sometimes you have to specify setting of Submenu’s width for better display*
Step 1 – name this Menu Item, then click Select to choose the Menu Item Type.
Step 2 – in the Menu Type selecting windows, please choose the External URL in the System Link group.
Step 3 – return to the Menu configuration window, you could setup a menu icon if you like. We showed how to do it in the previous section: [ How to add icon to your menu item]).
Step 4 – select Modules for Submenu Content
Step 5 – on the selection box, find and choose Contact Form module.
Please leave other parameters untouched and click the Save button.
Best Regards,
Huyen Tran