I will describe by points what needs to be done to reset the switch settings:
1) Connect to the switch through the console port. The standard parameters are 9600 bps (may be 115200 if configured), 8N1, without flow control.
2) Disconnect and connect power to the switch.
3) When the message “Press any key to enter Debug Mode with 3 seconds …” appears, you must press any key to enter debug mode.
4) Enter the command “atlc” after the “Enter Debug Mode”.
5) Wait for the “Starting XMODEM upload” message and send the configuration file. For Windows, you can use ExtraPuTTY for this, in Linux – Minicom.
The standard configuration file is usually in the archive with the firmware, it is with the .rom extension.
You can download from the official website www.zyxel.com
6) When the configuration file is loaded, enter the “atgo” command to reboot the switch.
See also my article:
How to transfer a file via XMODEM using Minicom