1. Navigate to Records
  2. Open the desired constituent record
  3. Select the Relationships tab
  4. Open the relationship record to add as a constituent.
  5. Select Relationship > Add this individual (organization) as a constituent from the menu bar

Spouses can also be added as a constituent from the Spouse button:

  1. Open the constituent's record
  2. Click the Spouse button
  3. Select Relationship, Add this individual as a Constituent from the menu bar

Additional Resource: 

NOTE: It is not an available option to do this for multiple records at one time within The Raiser's Edge.  This must be done individually from the specific relationship record.  It may be possible to utilize Professional Services to do this for a group of records, contact your Account Executive if interested in this option.