In order to hard reset a Nokia 7210, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Nokia 7210 device will be brought back to the default configuration of a brand new device.
1. Power up the phone.
2. Open the dialer, enter this code into it - *#7370# - and confirm.
3. Enter the lock code into the phone (12345 by default). Device will reset and restart.