Hello Larry-
Thanks for reaching out! If you’re talking about the Post & Page Builder editor, you can use the Revisions control to revert to previous versions of your post or page:
If you mean the Customizer, there aren’t revisions for those settings. Alternatively, you can use the Save Draft feature in the Customizer to make changes that you can easily revert:
Another way you can always be sure to have a “save point” is to use Total Upkeep to make and restore backups as you work on your site.