If you are planning to add a banner like this in your header, here are the steps to do it.

This option is available in only Header 3 layout.

Appearance > Customize > Affiliate Booster Theme Panel > Layouts > Header Layouts.

and select Header 3.

Once done, now go to Appearane > Widgets

Add image widget in this area and upload a 728x90 image.

Done. :)