When Undo History is enabled on entity, all updates to a record create a History activity record that will appear in the record’s timeline.
Opening the History record will display the changes that were made
To undo the change just click the Undo button in the ribbon bar. The change will be undone and a confirmation message will appear.
Click OK and the system will return you to the record in its new, state as it was prior to the update that has just been undone.