how to Change default gateway to 192.168.1.1 ? but cant access the current one 192.168.0.2!!

[sudipta_nov15]

I cannot set up bsnl broadband on a pc with windows 2000 installed. So my pc guy came and tried to do it. but at the same time he ended up changing the default gateway of my DNA-A211-I modem into 192.168.0.2, and cannot access the modem page using the default gateway address!
How can i change the Default Gatway to the original 192.168.1.1 or access it using 192.168.0.2?
How to connect broadband on a Win 2000 machine??