To add your secondary nav onto your page and have it sticky, use the data-position="section" option.

To do this, you’ll need to place your code within a code block on a section on your page, not in the Footer Code Injection area. Sticky is automatically turned on when this setting is used and this section will stick to the top of the screen (or bottom of your header) as a user scrolls down.

Note that this option cannot be used on collection pages.