1. Click "Settings" on the main interface of the machine to open "Flight Mode".
2. Open General in the Settings interface and select Restore:
3. Select Erase all contents and settings:
4. Restart the machine.
If it cannot be restored, you need to restore the system. The operation is as follows:
1. Apple official website downloads itunes on the computer and opens it after installation.
2. Connect the device to the computer with a data cable, and itunes will automatically install the driver after recognizing the device.
3. click "restore system" and follow the instructions in itunes to restore the system.