You would need to activate the module from Appearance >Nevo Options > Transparent Header.

After activating a module click on Customize > Header option to get started. Click to Transparent Header to open item settings.

Transparent Header Settings
-
- Enable on: Desktop or Mobile or Desktop + Mobile.
- Styling: custom item.
- Sticky Logo & Transparent Logo retina: exclusively for transparent header.
- Logo Max Width:
- Enable on …: choose to allow transparent headers on certain pages.