In order to hard reset a Ericsson GH 688, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Ericsson GH 688 device will be brought back to the default configuration of a brand new device.
1. Power up the device.
2. Go to Settings > Master Reset.
3. Type in the phone's lock code (0000 unless changed by the owner).
4. Press Yes. Done.