Set an example IP address for the other subnet as an alternate Seed IP Address in Properties and then enter the associated subnet mask. For instance;
if the IP for the machine running the application was 10.1.1.10 and the subnet mask was 255.255.255.0, it would scan 10.1.1.0 to 10.1.1.254.
If you changed the subnet mask to 255.255.0.0 it would scan from 10.1.0.0 to 10.1.255.254 (it actually scans this size range very quickly on SNMP discovery).
Alternatively you could enter a seed IP address and associated subnet to scan that network. Once clients have been added to the list they will always be monitored according to their IP address irrespective of subnet mask.
Finally, you can add any IP or URL manually via the Add function, thus if you had a client available across the internet you can still monitor it.