Interesting one here. I've got a google search appliance that no one has used for ages (yes, everyone knows it's end of life but they want it up) and I've no way of resetting it to factory defaults or even finding out what IP address has been configured on it.
Help! :-)
If you have direct access you can follow the instructions Google provides for configuring the GSA with a cross-over cable. That interface contains a place to view the current IP as well as change it.
However, the license is likely expired on it so it will not function for crawling/serving purposes. Likely all you can do is have Support wipe it and repurpose the hardware.