Table of contents:
Overview
If you come across duplicate Gem profiles for the same candidate, you can merge them together so that the candidate's data is combined into a single profile.
Requirements
The top of the Gem sidebar will surface the option to resolve duplicates if all of the following criteria are met on their profiles:
The candidate's First Name and Last Name fields match (not case-sensitive)
The candidate is not in an active sequence on any profile
At least one of the following is true:
The Primary Email Address on one of the profiles also appears in the Emails list for the other profiles.
The Company name matches on the profiles (not case-sensitive)
Merging profiles
When these conditions are met, the following notification will appear at the top of the Gem sidebar while viewing any of the profiles:

Clicking Resolve will take you to a page where the profiles are listed. You can pick and choose which candidate data fields will be saved to the final merged profile. When you are finished, click Save.

Limitations
Merging profiles can only be performed one candidate at a time
Potential duplicate profiles are not surfaced as a list in Gem (you will need to come across a duplicate profile to see the option to resolve and merge them)
First Name, Last Name, Primary Email and/or Company are the only fields that trigger the duplicate profile merging prompt
You cannot merge profiles if the candidate is in an active sequence on any of them