If you have configured Rumba+ Desktop to be the default TN3270 emulator ( ), it is launched when you right-click a server (associated with a Mainframe Subsystem application), from the Server Explorer view, and select Show TN3270 Display.
The session used to connect depends on the Use project specific Rumba session profile (if exists) option in the TN3270 preferences. If this option is selected, you can specify the path to a session profile file in the project's Properties view (see below). When located, this session profile is used upon connection. If the option is not selected or the specified file cannot be located, a default mainframe session profile is used.
See the Rumba+ Desktop product Help for more information on session profiles.