Header and Footer are special layouts which can be customized via builder editor. You can create as many layouts as you need and attach one default header and one default footer to your website in main settings.
To add or configure a header or a footer layout go to Pagex >Layout Builder. Here you can change and create header and footer layouts.
Set default Header or Footer
To set one of created header or footer layouts as a default one, navigate to Pagex > Settings. Then in a section Default Layouts you can choose which Header and Footer layouts will be used for your website.