Unlike in word processing programs, once you save a Joomla article you can't use ctrl-z to go back to a previous version. However, if you enable "versions" in your website, you will be able to access previously saved versions of your Joomla articles - depending on how you have things setup.
This video also refers to xbAutosave for autosaving article changes in Joomla.
Be sure to check out our video about that too! ► • Use xbAutoSave to Save Joomla Article...
How to turn on article versions and set it up correctly in Joomla and how to use this feature is what this Maintenance Monday live stream is about.