You should have stopped at the point that the new address didn't work.
If it is not some major problem, you can always sniff packets from the router to find the address. Even if there is no IPv4 configured, there will be link local IPv6.
Maybe it is not too late for that. Install wireshark on your PC, run it on the ethernet interface, connect the cable to the router and power it on. You should see some packets when the router boots and the network is enabled.