As you have probably noticed, there is no console port on the unit. If you can determine the IP address, your best bet would be to try to connect to it directly via SSH.
There is a tool to remotely reset the AP, but you need the serial number and the procedure must be completed within 10 minutes of a reset. This tool is for WiNG APs, and the 4600 was an OEM AP650 at the time, but I don't know if it will work or not. See: https://extremeportal.force.com/ExtrArticleDetail?n=000018658