Headers and footers are parts of the master page. For more information, see also Master pages. The content of the master page is repeated on every page of the document by default.
If required, you can specify that a different master page should be used for the first page of the document (including a different header and footer). This is useful, for example, when printing the first page of a letter on a preprinted letterhead and the remaining pages on normal white paper.
To do so, select the ribbon command Layout | Chapter 
and enable the option Different first page. From now on, the headers and footers on the first page can be edited independently of the rest of the document.