Thank you for contacting us!
Our team is happy to answer any questions you have about working with the Menus on your website.
The easiest way to create dropdowns while editing menus in your Customizer is to drag the appropriate menu items under their parent element to create the dropdown effect.
You can also use the Reorder option and indent the items using the arrow buttons in that interface.
We also have a guide in support center that goes a little more in depth on working with the Menu controls in the Customizer.
https://www.boldgrid.com/support/using-the-boldgrid-theme-framework-customizer/working-with-menus-in-boldgrid/
I hope this information helps you get your menus working as expected and please let us know if there is anything else that we can do to assist you!