Flutter: How to receive data from bluetooth manager class

Question

I'm building an app to communicate the mobile device with the external device over Bluetooth classic. I'm using the flutter_bluetooth_serial package. I'm able to connect to the device and also I'm receiving the data back. I created a Bluetooth manager class with a notifier, all the Bluetooth operations are handled in this class. Now, when I send a command/message from the "device firmware" class, data is received in the Bluetooth manager class, but I want data to be received in the "device operation" class. Likewise, If I send a command/message from "some other class", I should receive data on "some other class". Below is part of my code. Can somebody tell me how to achieve this?

BluetoothManager Class:

 class BluetoothManager extends ChangeNotifier {
      static final BluetoothManager _singleton = BluetoothManager._internal();
    
      factory BluetoothManager() {
        return _singleton;
      }
    
      BluetoothManager._internal();
      List<dynamic> globalFinalList = [];
    
    connectToExternalDevice() async {
        try {
          await BluetoothConnection.toAddress(device.address).then((result) {
           
            connection?.input?.listen(_onDataReceived).onDone(() { // _onDataReceived metod will receive data
             
            });
          });
        } catch (exception) {
          // TODO
        }
      }
    
    Future<List> _onDataReceived(Uint8List data) async { // This method received the output
        List<dynamic> finalList = data
        Uint8List uintList = Uint8List.fromList(receivedDecimalData);
        globalFinalList = finalList;
        return finalList;
      }
}

Device Firmware class:

void sendMessage() async { //This method sends command to the external device
    var commandhelper = CommandsHelper();
    var finalCommandWithCRC = await commandhelper
        .getCommandWithCRC(commandhelper.mainFirmwareCommand);
    var finalHexValues =
        await commandhelper.convertCommandToHexTwoBytes(finalCommandWithCRC);

    var finalCommandtoSend =
        await commandhelper.convertCommandToSignedDecimal(finalHexValues);
    Uint8List bytes = Uint8List.fromList(finalCommandtoSend);
    connection.output.add(bytes);
    await connection.output.allSent;
  }

Once the sendMessage()method is executed, _onDataReceived method in Bluettooth manager class will receive the data. But I want this message in the Device Firmware class