You would want to go to Configure> Users> Users (left hand side menu this time)> Check the box next to the user in question. If you want to see his current password or change it, click on the notepad icon at the top of the page to edit the user. You can un-obscure the current password or change the password here and save.
To re-deliver the current password to the user, assuming email delivery was enabled when creating the user group, you can go to the Users page and click on the email icon under the Delivery column to resend the email with the PPSK credentials to the user.
