In order to hard reset a Fly SL399e, you should perform the following steps.

Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Fly SL399e device will be brought back to the default configuration of a brand new device.

1. Make sure that the smartphone is turned on.
2. Tap in the *#987*99# code. Press Send.

3. Wait for the smartphone to restart.