Restore Previous Versions of Documents with SharePoint Online
When versioning is turned on in a SharePoint Online list or library, any changes you make to an item in a list or a file in a document library is stored as a version, allowing you to manage content as it goes through various iterations.
This is especially helpful when you have multiple users editing a document. If you run into a scenario where you have to roll back to an older version of the file, all you have to do is select a version from the version history that you want to restore.
To turn on version control for any document library, follow these steps:
Go to your Shared Documents library.
On the Ribbon, click Library.
Click Library Settings.
Below General Settings, click Versioning settings to view all available options from the Versioning Settings page.
Below Document Version History group, select Create major versions.
Click OK to complete the versioning control process.
Now that you’ve turned on version control, you can view the history of a document and restore a previous version as follows:
In your document library, click Library below Library Tools and then click Library Settings on the Ribbon.
Hover over the name a file in the library until you see the down arrow.
Select Version History.
The Version History window appears with a list of the versions stored for the file.
Hover over one of the dates until you see the down arrow on the right.
Click the arrow to bring up the View, Restore, and Delete options for the version.
Click OK after you make your selection.
Instructions for restoring an item in a list is similar to how you restore a file in a document library.