How to open the internal tag

Use the string "nfc:InternalPlainTag", for instance:

...
InternalPlainTagConnection conn = (InternalPlainTagConnection)Connector.open("nfc:InternalPlainTag");
...

Note: Check first if the external scan is already activated to disable it:
...
import com.nxp.software.nfc.InternalPlainTagConnection;
import com.nxp.software.nfc.ExternalScan;
...
if ( ExternalScan.isStarted() == true ) {
  // Scan is already started need to stop !
  ExternalScan.stop();
}
pconn = (InternalPlainTagConnection)Connector.open("nfc:InternalPlainTag");
if (pconn == null) {
  // Connection failed
  return;
}
...

In the integration guide you will able to find more information.