How to change the header and edit other Single pages of Portfolio items settings?
All single portfolio items inherit the settings from their template page. In order to edit excerpt text and header background image, please locate this page on All Pages list, and proceed to follow instructions from our article.
In order for this page to work as a template page for single portfolio items, make sure to add its slug to Settings Page Slug field in Appearance >Customize >Portfolio panel.
For more info and detailed instructions please refer to our Online Theme Documentation.