Header Image bug? How to fix it?

I would ask you this question if support for the template did not answer my question. I use a strange template and as I know, I’ve set Header Image, and the problem is that. (Long ago anyway, but now we want to fix any such minor problems)

So if I write an article and want to share it somewhere (Facebook, Twitter), it does not focus on the image of the article (Featured Image), but the Header Image and appears as the “main image”. Sometimes, on Facebook, though, it’s a good idea to switch between images, but not at Twitter and elsewhere.

Image roughly: https://kephost.com/images/2017/08/16/A25S7s-cQqS1tNUQM74I1A.png

The page I need help with: [log in to see the link]