Each Corda node individually advertises the services they offer and are setup via the node config and Gradle files.
If you're running from unit tests and using mock nodes, you'll find the advertised services are configured per mock node. With DemoBench, the services are defined within notary.conf under demobench_main.
You shouldn't have to change these though. Any CorDapps you load into DemoBench will also be run on each node in addition to the services selected.
I would suggest taking a look at the more simpler CorDapp examples, such as those found at https://github.com/roger3cev (iou-cordapp-v2 is a good one) as a starting point and running them outside of DemoBench while you're still finding your feet