Accessibility - Updating Page Templates to include Landmarks

I am in the process of updating a site to better support WCAG standards.
One of the items I would like to add is “landmarks”

Essentially this requires adding roles to different sections of the page templates.

This is the header
This is the nav
This is the main
This is the footer

I know I can edit the theme layout files directly, but I suspect there is a way to overlay these div tags to existing elements on the page, but I’m not sure how to go about this.