How can I add an image to my header home page

Hello!
I’m very new and can’t find info on how to load an image that will show up behind and below the header. I can see this is an option in Highend but can’t find the video or documentation on how to do it 🙂

The website is in coming soon mode (in case that matters)

BTW – Highend is a great product, I’m so happy I purchased it! And your support has been awesome too!

Thanks,
Kalee