Overview
Contact forms can be added using Contact Form 7 or any form plugin of your choice that provides a shortcode.
Just paste the shortcode provided into either a Custom Content item (recommended) or a Text Widget.
You will almost certainly want to add this to a second level menu item in order to make it appear in your submenu.
Note that the contact form styles will be inherited from your theme or your form plugin.
Contact Form Custom Content
Result:
