Hi Avander, when enabling multiple subnet you will type in the IP address and a subnet mask. So if you type in 192.168.2.1 with 255.255.255.0 mask, then 192.168.2.1 becomes the default gateway for that subnet. The router will still maintain its original IP address. So if you're managing the router through 192.168.1.1 that will remain the router's IP address.
-Tom
Please mark answered for helpful posts
http://blogs.cisco.com/smallbusiness/