Popups: How To Add A Header Popup
Popups can be added to the header using Divi MadMenu Button elements, this feature is available since the v1.6 of Divi MadMenu.
Header popups are created and edited in the same Divi Theme Builder header template as the header itself that you want these popups to be added to, so, you do it all in one place. Any builder element(section, row, column and module) can be used to create a header popup, however, creating popups using sections is recommended.
Here is a quick tutorial about how to add a popup to the header: