transparent secondary navigation merge

I am merging a seperate page header into the homepage layout.

This header has a transparent background, which I want to replace both primary and secondary navigation in the header below.

And that's the problem.

https://i.imgur.com/lqpPKxd.png

The separate page header only has primary navigation and I can't find any way to add secondary navigation.

As a result, the new header doesn't have a secondary navigation, so it still shows the original secondary navigation, and in its original color background.

Is it possible to merge a separate page header where both the primary and the secondary navigation backgrounds are transparent, thus allowing the page's full height image below to be completely visible, with transparent primary/secondary navigation?

If so, how? {pretty please}