Try this method:

1)  Switch your Contacts folder to a table view (unfiltered).  It's easiest
if the view is not already grouped by any fields.  OR, create a new view
just for this purpose so you don't mess up any of your existing views.

2)  Go to View | Current View | Customize Current View and click the Group
By button.  In the "Select Available Fields From" dropdown near the bottom,
select "All Contact fields".  Then in the first "Group items by" box, select
Private.  It's up to you if you want to check the "Show field in view" box
or not.  Click OK twice to exit the customize view dialog.

3)  You'll now see your contacts grouped by whether they are private or not
private (some may say "None").  If none are marked not private, change the
value for one of the contacts so that it's not private, and a group will be
created.  Now all you have to do is drag the private items to the
non-private group to change the privacy status.