Changing Header Image

I would like to be able to use an image as the header on my individual pages/posts and blog header. Currently the theme defaults to a black header for the blog page and a white one for other pages. I have tried to find the coding necessary to change it, but have spent countless hours to no avail. Any help would be appreciated!

If I use the ‘add header’ customizer, it adds the header to the front page, which I do not want.

My site is https://www.tampashorescommunitychurch.com. Thanks!