How can I reset all personalization changes made by a specific end user?

Your end users can personalize a page explicitly (like creating a saved search) or implicitly (like changing table column width). You can revert all such changes made by a specific user using the Personalization page in Application Composer.

In the Common Setup region, click Personalization. Search for a user and then click Reset Personalization. All changes made by that user are removed and all pages are restored to the default content and layout as originally delivered. Changes implemented by an administrator using Application Composer and Page Composer are retained, if they exist.

End users can also revert their changes themselves, but only on a page-by-page basis.