In order to hard reset a BlackBerry Style 9670, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
BlackBerry Style 9670 device will be brought back to the default configuration of a brand new device.
1. First, power up the phone by pressing the Power button.
2. Open All tray.
3. Choose Options > Security > Security Wipe.
4. Tap in the word "blackberry" when asked to. Select the Wipe Data.