By default, when launched, the TN3270 mainframe display automatically connects to the enterprise server associated with your application.
When using the embedded Mainframe Rumba+ Desktop Display view, you can have more than one active connections at the same time, but the display is only showing one of them. To connect to a different enterprise server from the ones to which you have already been connected:
This connects the display to the respective server and loads the application in it.