Unfortunately, Checkbook Pro doesn't have a feature to reset the password. I suggest you to uninstall the application and to reinstall it. You can download it again from its official web page. If you have lost the serial number, you will need to send a message with the name and email address used to place the order to
email@example.com. Since the password protection option is not mandatory, I suggest you to use it only if your computer is accessed by multiple users.