Android DFPlayer Mini Bluetooth control

#include <BluetoothSerial.h>
#include <Arduino.h>
#include <DFRobotDFPlayerMini.h>
DFRobotDFPlayerMini myDFPlayer;


BluetoothSerial SerialBT;

#define BT_DISCOVER_TIME	10000
int action = 0;
int Song = 0;
static bool btScanAsync = true;
static bool btScanSync = true;

void btAdvertisedDeviceFound(BTAdvertisedDevice* pDevice) {
	Serial.printf("Found a device asynchronously: %s\n", pDevice->toString().c_str());
}

void setup() {
 Serial2.begin(9600);
 Serial.begin(115200);
  if (!myDFPlayer.begin(Serial2)) {  //Serial2 to communicate with mp3.
    Serial.println(F("Unable to begin:"));
    Serial.println(F("1.Please recheck the connection!"));
    Serial.println(F("2.Please insert the SD card!"));
    while(true);
       delay(0); // Code to compatible with ESP8266 watch dog.   
  }
    Serial.println(F("DFPlayer Mini online."));
  
  myDFPlayer.setTimeOut(500); //Set serial communictaion time out 500ms
  
  SerialBT.begin("ESP32"); //Bluetooth device name
  Serial.println("The device started, now you can pair it with bluetooth!");


  if (btScanAsync) {
    Serial.print("Starting discoverAsync...");
    if (SerialBT.discoverAsync(btAdvertisedDeviceFound)) {
      Serial.println("Findings will be reported in \"btAdvertisedDeviceFound\"");
      delay(10000);
      Serial.print("Stopping discoverAsync... ");
      SerialBT.discoverAsyncStop();
      Serial.println("stopped");
    } else {
      Serial.println("Error on discoverAsync f.e. not workin after a \"connect\"");
    }
  }
  
  if (btScanSync) {
    Serial.println("Starting discover...");
    BTScanResults *pResults = SerialBT.discover(BT_DISCOVER_TIME);
    if (pResults)
      pResults->dump(&Serial);
    else
      Serial.println("Error on BT Scan, no result!");
  }
  myDFPlayer.volume(10);
}

void loop() {
  action = SerialBT.read();
  if (action != -1) {
 Serial.println (action);    //Print what we receive 

    switch (action) {
      case 1:
       myDFPlayer.previous();  //Play previous mp3
       break;
       
       case 2:
       myDFPlayer.pause(); //Stop
       Song = 0;
       break;
       
       case 3:  
       if (Song == 0) {
        myDFPlayer.play(1);  //Play from beginning  
        myDFPlayer.enableLoopAll();
        Song = 1;     
       }
       else {
        myDFPlayer.start(); //Play from Pause
        myDFPlayer.disableLoopAll();
       }
       break;
       
       case 4:
       myDFPlayer.pause(); //Pause
       break;
       
       case 5:
       myDFPlayer.next(); //Next
       break;
       
       case 6:
       myDFPlayer.volumeDown(); //Volume +
       break;
       
       case 7:
       myDFPlayer.volumeUp(); //Volume -
       break;

       case 8:
       myDFPlayer.EQ(DFPLAYER_EQ_NORMAL);
       break;

       case 9:
       myDFPlayer.EQ(DFPLAYER_EQ_POP);
       break;

       case 10:
       myDFPlayer.EQ(DFPLAYER_EQ_ROCK);
       break;

       case 11:
       myDFPlayer.EQ(DFPLAYER_EQ_JAZZ);
       break;

       case 12:
       myDFPlayer.EQ(DFPLAYER_EQ_CLASSIC);
       break;

       case 13:
       myDFPlayer.EQ(DFPLAYER_EQ_BASS);
       break;

       case 14:
       myDFPlayer.loopFolder(1);
       break;

       case 15:
       myDFPlayer.loopFolder(2);
       break; 
           
       case 16:
       myDFPlayer.loopFolder(3);
       break;
       
       case 17:
       myDFPlayer.loopFolder(4);
       break;
       
       case 18:
       myDFPlayer.loopFolder(5);
       break; 

       case 19:
       myDFPlayer.loopFolder(6);
       break; 

       case 20:
       myDFPlayer.loopFolder(7);
       break;

       case 21:
       myDFPlayer.loopFolder(8);
       break;
       
       case 22:
       myDFPlayer.loopFolder(9);
       break;

       case 23:
       myDFPlayer.loopFolder(10);
       break; 
                      
    }
    
  }
  }