Factory resetting Yealink phones can be done using the handset or base station.
To reset your T4 series handset, ensure your phone is at idle (no calls in progress, or any notifications for voicemail, etc.)
Press and hold the OK key for about 8 seconds, until you receive the 'Reset to Factory' prompt, then press OK to confirm the reset.
To reset your T5 series handset, ensure your phone is at idle (no calls in progress, or any notifications for voicemail, etc.)
If your handset has an OK key, press and hold this for about 8 seconds, until you receive the 'Reset to Factory' prompt, the press OK to confirm the reset.
If your handset does not have an OK key, press and hold the 'Redial' key for about 8 seconds, until you receive the 'Reset to Factory' prompt, and press the Accept key.
To reset your Yealink cordless, locate the base station, then remove the power. Hold the 'Connect' key and power back up, while continuing to hold Connect.
Once all 3 lights are illuminated, release the connect button. Your unit will now reset.
If your cordless handset loses its pairing with the base station, you can reconnect it by pressing the connect key until the 'Registration' indicator flashes, then press Reg on the handset.