Drupal automatically creates a back-up copy of the previous versions of pages you’ve edited.
If you want to revert to a page’s previous version, click on the Revisions tab next to the View and Edit tabs at the top of the page you want to edit:
You’ll see a list of Revisions:
Click on the Revert link to the right of the relevant revision to restore the page’s content to that previous version.
⚠ Tip: Not sure which version of the page is the right one? You can view any of the revisions by clicking on their date and time. For example, in the screenshot above, you would click on “Mon, 10/23/2017 – 10:50” to view a snapshot of that version.