Perform a soft, factory, and alternate master reset of the device.
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INSTRUCTIONS & INFO
A master reset reverts the device back to factory settings. It will permanently erase all personal data, preferences, settings and content such as pictures, ringtones and apps that are saved to the device. Data stored to an SD card (sold separately) will not be erased unless otherwise selected. It is recommended that you save (backup) important data to your SD card, SIM, cloud services (for applicable devices), or a computer before proceeding. See the 'Backup & restore' tutorials for more information. To power cycle your device, press and hold the Power button, then tap Power off.
To perform a device restart, press and hold the Power button, then tap Restart.
To perform a factory data reset (master reset), swipe down from the top of the screen, then tap the SETTINGS icon.