If the participant has their own constituent record:

  1. Go to the Participants tab of an event
  2. Double-click the participant name that is not showing in bold
  3. Click the '...' button in the Registrant field
  4. Click the binoculars button beside the Last Name field
  5. Search for the participant's constituent record
  6. Click OK and save the participant record

If the participant does not have their own constituent record, you can create a Constituent record for them.