When editing some The7 demos, you may also notice that footer and header areas are managed as a separate Elementor section marked with yellow (fig. 1):
This is a footer/header template, it allows to create custom layout (which might be not available with theme tools) and edit it from one place: Dashboard -> Templates -> Theme Builder (fig. 2)
You can edit existing templates here and create new ones in accordance with Elementor documentation. Templates are available for header, footer, content area and archives.