On an Avaya IP Office, the administrator password can be changed on the Security tab on System settings. This tab can be accessed by selecting System > Security, and then clicking on the Security tab. On the Security tab, you can enter the new password for the Administrator account, as well as configure other security settings. The administrator password cannot be changed by selecting resources on SSA, using CLI commands when accessing the DTE port, or on the Security settings.
Reference:
Avaya IP Office (https://www.avaya.com/en/solutions/ip-office/).
Avaya IP Office System Security (https://www.avaya.com/en/solutions/ip-office/system-security/).