Go to People > All People.
In the filter dropdown, expand on Status, and select ‘Archived’. Click the ‘Apply’ button to reload the list of people.
In Table View:
Click the ‘Mark as Active’ or ‘Mark as Contact’ link underneath the the person you wish to reactivate.
In List View:
Click the ‘Mark as Active’ button, or select the Drop down to Mark as a Contact.
Once an option has been selected, you’ll be taken to the person’s profile for any additional edits.