Sometimes people manage to register themselves twice! So admins can check the directory for any issues from the main admin screen (from v3.4.105)
Click the “Check for directory issues” button. After a few seconds, the next screen will show you any issues with options to fix. This article covers the issue of duplicate records.
The first occurrence in the database is the one that stays. You can click on Display household to check the entries.
If you click on Merge, the next screen will show how the merge will happen.
You can check each row and change which column will get saved. When you have clicked “Merge” at the bottom, your choices are saved to the left hand entry and the right hand one is deleted. The first person’s ministries, classes and groups are kept and the second person’s deleted.