If you merged two records by accident and would like to undo, or revert that action you can do so under the ‘Team> Activity Log‘ area.
In the Activity Log, you should see two merge actions one called Merge-D and another called Merge-U.
To perform the unmerge, click the ‘Undo‘ option for the Merge-D record first, then click the ‘Undo‘ option for the ‘Merge-U’ record.