showNotification(notificationMessage, customAction);

kullanarak üsttende gösterebiliriz

@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
    String notificationMessage = remoteMessage.getNotification().getBody();
    String customAction = remoteMessage.getData().get("customAction");
    showNotification(notificationMessage, customAction);
}

private void showNotification(String message, String customAction) {
    Intent intent = new Intent(this, YourTargetActivity.class);
    intent.putExtra("notificationData", message); 
    intent.putExtra("customAction", customAction); 
    PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, CHANNEL_ID)
            .setContentTitle("Başlık")
            .setContentText(message)
            .setSmallIcon(R.drawable.ic_notification)
            .setContentIntent(pendingIntent);

    NotificationManagerCompat notificationManager = NotificationManagerCompat.from(this);
    notificationManager.notify(notificationId, notificationBuilder.build());
}

bundan sonra onCreate veya onNewIntent kullanmamız gerek

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_your_target);

    if (getIntent() != null && getIntent().hasExtra("notificationData") && getIntent().hasExtra("customAction")) {
        String notificationMessage = getIntent().getStringExtra("notificationData");
        String customAction = getIntent().getStringExtra("customAction");

        if ("goToFragmentA".equals(customAction)) {
             navigateToFragmentA(notificationMessage);
        } else if ("goToFragmentB".equals(customAction)) {
            navigateToFragmentB(notificationMessage);
        }
    }
}

private void navigateToFragmentA(String message) {
      FragmentA fragmentA = new FragmentA();
}

private void navigateToFragmentB(String message) {
    FragmentB fragmentB = new FragmentB();
}