By default, when launched, the TN3270 mainframe display connects automatically to the enterprise server associated with your project.
If you are using the embedded Rumba+ Desktop display and it is not configured to connect automatically, when you launch the display you need to connect it to the server manually by clicking the Connect button .
This is the behavior when you are trying to connect to a server and the display is already in use and is connected to a different server:
Closing Rumba+ Desktop disconnects all active sessions.