Hello @informaticaaliverniniprogetti-it,
In order to add the additional custom menu in between the top header and primary menu requires a higher code customization and as much as we would love to help you with this we are unable to do so as it requires higher code customization.
So our suggestion to you is higher a professional developer so that the theme is not affected in any way.
To hire a developer please follow below-given link:
http://themepalace.com/hire-a-customizer/
Thank you 🙂 .
Best Regards!!