If you have two similar contacts and would like to migrate all the data into one record, you can follow these steps.
Navigate to the duplicate contact you do not wish to keep (or the one with the least amount of emails and notes on the timeline).
For any emails on that timeline, you can open the timeline tray (the briefcase icon to the right of the "i" icon). From there you can add the email to another contact timeline, and then remove it from the current timeline.
For notes, you can copy and paste the details in the notes or simply open the Note options menu and select, "move".
Copy and paste any detail information to the contact you are wanting to keep.
If you have any work that needs to be transferred, you can go to the work item menu ("...") and select Change client.
Once you have gone through and moved all details, notes and emails to the other duplicate contacts, you can delete the contact you no longer need.