exPressit SE is a very old application that was discontinued a long time ago. Because of that, troubleshooting and configuration can be very hard since nothing is available in terms of usage guides and manuals. The only thing you can access to configure your labels is the built-in Help section (if it has one). I've searched the web, but nothing was available.
Try using the dedicated application released by Avery Corporation when it comes to label printing and designing.
