Hello,
The addHeader method allows to set the default, even and first headers: https://www.phpdocx.com/api-documentation/layout-and-general/insert-headers-Word-document-with-PHP
The easiest solution to accomplish what you need is using the mergeDocx available in Advanced and Premium licenses (setting headers and footers per section as MS Word does and merging the documents to get a single DOCX):
https://www.phpdocx.com/documentation/cookbook/headers-and-footers-for-sections
Regards.