If the source of the menu set to ‘None’, just click on the item in the menu, go to Interactions section in the sidebar and select open dropdown. From there you can easily rename the items, link them to any page you want, duplicate, delete, whatever.
If the source of the menu is set to ‘Primary Menu’, open the menu manager, add a new menu with the links you want to appear in the dropdown menu, then go back to the primary menu and select the link you what to open the dropdown menu, then edit the type to ‘Open Menu’, and select the dropdown menu you just created.
If it’s too confusing for you, let me know. I will record the video for you.