Preferred given name for contact
You can change the display name for a contact in 2 ways

By using CiviCRM alter display name hook you can change the Display name to a preferred name.

Update the format for Sort name and/or Display name by navigating to Administer &gt;&gt; Customize Data and Screens &gt;&gt; Display Preference (civicrm/admin/setting/preferences/display?reset=1) and then update the 'Individual Sort Name Format ' and 'Individual Display Name Format' fields as per your choice.
(Note: This change will be reflected to contact only if New Individual is added or updated)


HTH
Pradeep