In order to hard reset a Panasonic KX-TU311, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Panasonic KX-TU311 device will be brought back to the default configuration of a brand new device.
1. Turn on the phone.
2. Continue to Menu. Then select Settings > Security > Reset > All Reset.
3. Provide the 4 digit code. Confirm it with Ok button.
4. Device will now reset and restart. Done!