How can I reset the password that locks the app and protected files?
The only way to reset the password is to delete then reinstall the app. This will delete all files currently stored in the app, so we recommend you transfer these files to a computer using iTunes File Sharing before deleting the app (see this page for details on iTunes File Sharing). Make sure your device stays unlocked (with the screen on) during the transfer (this is required to transfer protected files). After reinstalling the app you can transfer your files from your computer back to USB Disk using iTunes File Sharing.