Leads/Prospects/Customers import to update the External ID > Error Message: This entity already exists

When performing a CSV Import to update the Leads/Prospects/Customers External ID, the following error is encountered and the import is not successful if there is another entity that already uses the External ID:

Error = This entity already exists.

To find the record that uses the External ID, create an Entity Search:

1. Navigate to Lists > Search > Saved Searches > New.
2. Click Entity.
3. Enter a Search Title.
4. Under Criteria > Standard subtab, add the following:

• External ID is XXXXX (Replace XXXXX with the External ID
  that encountered the error in the CSV Import)

5. Under Results > Columns subtab, add the fields to display in the search result, for example:

ID
Name
Type

6. Click Save & Run.

To resolve the issue, the External IDs in the CSV file can be edited to add a character/s.