You can help them reset their password in the same way the viewer would do it themselves. In this case, go to wherever your have placed your paid content (it doesn't have to be on the same webpage, all the client information is linked in the cloud when you charge). Click the "Paid? Login Here" tab on the right inside the player. Now enter in the viewer's email address and click "I Lost My Password" like below:
This will email the viewer a new password from the provided email address. Please make sure it's not being blocked by spam filters or other settings.