change view of an activity from another class

I am making an audio recording app and my MediaRecorder instance starts to run from a service, so that it even runs in the background, now I want to implement a timer to mark and save the recorded time, but how to activate the timer in my Service class and display the timer counter in my activity? Or do you have a better way to start the timer? I opted not to let running from the activity pq in the activity it would not mark the time if the app is in the background.

below is my code: my service class

package com.example.administrador.myapplication;

import android.app.IntentService;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.media.AudioManager;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.os.Environment;
import android.os.IBinder;
import android.support.annotation.IntDef;
import android.support.annotation.Nullable;

import java.io.IOException;

/**
 * Created by Administrador on 27/06/2017.
 */

public class TesteService extends Service{
    MediaRecorder mediaRecorder;
    PathFile pathFile;
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        pathFile = new PathFile();
        String file = pathFile.generateFileName();

        mediaRecorder = new MediaRecorder();
        mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);

        mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
        mediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
        mediaRecorder.setOutputFile(Environment.getExternalStorageDirectory().getAbsolutePath()
                + "/"+file+".aac");
    }

    @Override
    public int onStartCommand(Intent intent,int flags, int startId) {
        try {
            mediaRecorder.prepare();
            mediaRecorder.start();
        } catch (IOException e) {
            e.printStackTrace();
        }
       return START_STICKY;
    }

    @Override
    public void onDestroy() {
        if(mediaRecorder != null){
            mediaRecorder.stop();
            mediaRecorder.release();

        }
        super.onDestroy();
    }

    public void onComplete(){
        if(mediaRecorder != null){
            mediaRecorder.stop();
            mediaRecorder.release();

        }
    }
}

and I want to display a timer in the layout of this my fragment:

package com.example.administrador.myapplication.fragments;


import android.content.Context;
import android.content.Intent;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;

import com.example.administrador.myapplication.MainActivity;
import com.example.administrador.myapplication.R;
import com.example.administrador.myapplication.TesteService;

import java.io.IOException;


/**
 * A simple {@link Fragment} subclass.
 */
public class HomeFragment extends Fragment {

    MediaPlayer mediaPlayer;
    Button start,stop,play,stopPlay;
    public HomeFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
         View rootView = inflater.inflate(R.layout.fragment_home, container, false);
pathFile = new PathFile();
    String file = pathFile.generateFileName();


        start = (Button) rootView.findViewById(R.id.start);
        stop = (Button) rootView.findViewById(R.id.stop);
        play = (Button) rootView.findViewById(R.id.play);
        stopPlay = (Button) rootView.findViewById(R.id.stopPlay);


        Toast.makeText(getActivity(), Environment.getExternalStorageDirectory().getAbsolutePath(), Toast.LENGTH_SHORT).show();

        start.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent intent = new Intent(getActivity(),TesteService.class);
                getActivity().startService(intent);
            }
        });

        stop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Toast.makeText(getActivity(), "Recording Complete", Toast.LENGTH_LONG).show();
                Intent intent = new Intent(getActivity(),TesteService.class);
                getActivity().stopService(intent);
            }
        });

        play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                mediaPlayer = new MediaPlayer();

                try{
                    mediaPlayer.setDataSource(Environment.getExternalStorageDirectory().getAbsolutePath()
                            + "/"+file+".aac");
                    mediaPlayer.prepare();
                }catch (IOException e){
                    e.printStackTrace();
                }
                mediaPlayer.start();
                Toast.makeText(getActivity(), "Reproduzindo Musica", Toast.LENGTH_SHORT).show();
            }
        });

        stopPlay.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if(mediaPlayer != null){
                    mediaPlayer.stop();
                    mediaPlayer.release();

                }
            }
        });
return rootView;
    }

}

I know that to add a timer just insert it in layout.xml and in my fragment create an instance of it, associate with findViewById (); and give the start and stop. but I wanted the timer to remain in the background, so I thought about letting my service take care of it, but how can I insert it in the view of the fragment from the service?