How to add a banner image to modxblog theme?

I am trying to add a banner image (936x220px) to the modxblog theme but I am not sure where to start. I have the site on theme test drive, so you will see a different theme if you go to my site. However, I have found another site that uses the theme: https://paulrriddick.com/

Here is the image I would like to make my banner: https://butthegameison.com/blog/wp-content/uploads/2010/03/Banner_Mark_Travis_Final-2.jpg

The main problem I had was that the header for this site is not just a banner, but it also includes space for an RSS image and the page tabs (https://paulrriddick.com/wp-content/themes/modxblog/images/header1-bg.png)

Any and all help is appreciated.