With SharePoint, it is possible to view the previous state of a file, the changes that are made, and the user's that make those changes.
Note:
It is recommended that before you restore a file to a previous version, that you make a copy of the file first so that the most recent changes do not go away. After reverting the file, you will not be able to undo this change.
Version controls are typically accessed from the SharePoint Online interface. Navigate to the file that you would like to check the history on, select the 3 dots next to the file name,
You will be presented with the following
You can see when changes were made, and by who. Clicking on the date stamp for a particular change will present you with the option to view, restore, or delete.
Restoring will replace all changes that have come after the specified time irretrievably.