Replace features with header image

Wordpress and Arcane allows us to upload 2 tips of images: Featured and Header.
Currently, arcane is using
* the featured image in the article (a banner on top of the blog text)
* the featured image when displaying news block on an index page (wide image)
* does not use header image.

One image cannot be used as banner and landscape and both to look good. Apect ratio is important.
Therefore, I’d like to know how I can replace the image in the article (the banner one) to be taken from the “header image” upload (as it is indeed a header).

I’m fine with coding it myself if told how, but I am sure EVERYONE would appreciate this