Hello,
For that you can create networks and then force the election on one or more hosts and assign them to a specific network :
Go to the web page, Network(s) --> Administer, then Add, and here you create the network(s) you want to scan, enter the IP etc...
After that go to the host you want to elect for IpDiscover, Configuration --> Edit --> Network scan, and then in the IpDiscover line choose the network you want him to scan (he will be elected for the network you assign him to).
Normally its that way.
Regards.