Yealink T55a phone factory reset
If you can't get into the website for the phone (with default of admin admin) or get to the settings panel of device to reset with default of admin (password) 0000
You can reset the device to factory settings with the need for entering the Administrator's password. Procedure 1. Go to (More) > Settings > Device Settings > Debug (Admin only, default password: 0000). 2. Tap Reset to Factory Settings. It prompts if you are sure to reset to factory default. 3. Tap OK. Tip: You can also long press the pound key (#) and the star key ( * ) for about 6 seconds when the phone is idle.