Steps
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Reboot the system by pressing "Power" and "Volume down" simultaneously
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Boot menu should appear, use "Volume up/down" to select the menu item "Android Recovery", "Power" to confirm
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System reboots, a screen appears with a message "No command" - this is no error though it looks like one
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Press "Power" and "Volume up" together and a menu "Android Recovery" appears
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Use "Volume up/down" to select the menu item "Wipe data/factory reset", "Power" to confirm
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User data on the device is deleted and the original meu is shown
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Select the menu item "Reboot system now" and confirm by pressing the "Power" Button
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The device reboots and you may configure the Android system …