Adding a Secondary Heading in 7.1

I want to add a secondary heading bar below the primary one that will contain dropowns in them?

Like this but with the ability to have dropdowns in the secondary header rather than just static page links: https://www.will-myers.com/articles/add-secondary-navigation-to-your-squarespace-71-website

What is your site url? Do you use Personal or Business or Commerce Plan?