Some switches don´t have a "Reset" button on it. If you would like to reset the device to factory defaults, the simplest way is to login to CLI mode and use the command below to reset the device:
1)ES-2108-G# erase running-config
2)ES-2108-G# write memory
(This is just an example what will be displayed when logging into an ES-2108-G)
Please use Putty on Windows or a similar SSH client to login into your switch. You would need to type in the IP of the switch in the client. You will get asked to enter the username and password for your switch.
For other switch types, we often offer CLI-Reference-Guides on our FTP Server: ftp://ftp.zyxel.com
Search for the device folder of your switch and check if there is such a guide. For further help, please feel free to reach out to our support team!