Slider Volume updation after returning to main menu from a different scene

gistfile1.txt

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SliderVolumeValue : MonoBehaviour {

    static SliderVolumeValue instance = null ;

    private void Awake()
    {
        if (instance != null)
        {
            Destroy (gameObject);
        }
        else
        {
            instance = this;
            DontDestroyOnLoad (gameObject);
        }
    }

  
    // Reference to Audio Source component
    public AudioSource audioSrc;

    // Music volume variable that will be modified
    // by dragging slider knob
    public float musicVolume = 0f;

    
        

    // Use this for initialization
    void Start()
    {

           // Assign Audio Source component to control it

            audioSrc = GetComponent<AudioSource>();

     }
    

    // Update is called once per frame
    void Update()
    {

        // Setting volume option of Audio Source to be equal to musicVolume
        audioSrc.volume = musicVolume;
        PlayerPrefs.GetFloat("musicVol", musicVolume);
        

    }

    // Method that is called by slider game object
    // This method takes vol value passed by slider
    // and sets it as musicValue
    public void SetVolume(float vol)
    {

        musicVolume = vol;
        PlayerPrefs.SetFloat("musicVol", musicVolume);
        PlayerPrefs.Save();
        
        

    }

   
   
}