Connect a serial cable to the console port.
Setup a communications software to 38400 bps,8 bits,no parity.
Verify that you could “talk” to the box by pressing “enter” several times.
Whith the software running, reset power to the box.
it wil display a message at one point saying something like “press enter to enter configuration”.
By doing that, you will reset the box to factory default, erasing the configuration and password.
You are now ready to start from scratch.