Thanks for posting in! Please understand that Cornerstone is a page builder. You can create a page or post using Cornerstone. You must be aware that archive pages were dynamically generated by WordPress. You cannot edit the archive page with Cornerstone or even the default WordPress editor.
If you need to have a custom archive pages, please check out these threads: https://developer.wordpress.org/themes/template-files-section/taxonomy-templates/#taxonomy-template-hierarchy
You can place a custom template on the root directory of your child theme. This allows you to make code changes that won’t be overwritten when an X update is released. After your child theme is setup, please review how we recommend making template changes in Customization Best Practices.
Hope this helps.