Most of Uncode demo headers are made with the native Content Block module and are connected to a single page by the Page Options > Header tab, you find this options panel at the bottom of every page, post, portfolio or product page, screenshot.
Headers are external to pages. They can be linked to a single page or can be reused and shared among multiple pages as "matrix" for the header layout. With the Content Block you can create headers the same way you work with Visual Composer. You can check those reference:
Important note: If you access the Content Block editor and you don't see the Page Builder but you see only codes, you have forgot the step 7 of the installation procedure.