After you have created your custom shortcode on functions.php, follow these steps to add this shortcode you created into your navigation menu:
Go to Appearance → Menus.
Add a Custom Link.
In the URL field, just put # (it won’t be used).
In the Navigation Label, paste your shortcode for example :
[button_row]
[instagram_icon_button_gelateria]
[instagram_icon_button]
[/button_row]
Click save your menu.