To reset the handheld to factory default, you have to press and hold the reset button that can be accessed through a small hole inside the battery compartment (chapter 4.1). You will hear a sound when the reset has been initiated.
To access the button a very thin object (i.e. paperclip) is required. After resetting, the handheld is in factory configuration. No data in the OccluSense®-iPad-App is being deleted or changed.