the preview image shows in the header and how to delete it?

Hi … Would anyone advise why the preview image is displayed in the header and how to remove it from there? (from every page).
I need a preview image to show the images in the POSTS section because otherwise I would only have text there.
And another image should be displayed in the header, such as the one I specify in the “Header Image” for each page.
Maybe more information will be needed to clarify the problem, so if there is someone who would like to advise me and needed more information, just ask …