SharePoint Online offers the ability to restore files to previous versions.
Navigate to the file on SharePoint Online. Select the Show Actions icon.
Select Version History from the drop-down menu. This will open the Version History window.
Clicking on the different versions will open them in read-only mode.
Your browser may ask for confirmation when opening another application.
To restore the version, select the menu arrow and then Restore
You can also restore Office application files from within the application itself if the file was saved to SharePoint.
In the Office application (Word, Excel, etc) select File, then Info
Then select File History
This will open the Version History panel. Select which version you want to view.
Learn more on the Patriot Knowledge Center: Microsoft SharePoint