How do I switch background music using AVFoundation in Xcode?

import UIKit
import SpriteKit
Import the import AVFoundation // AVFoundation framework.

classGameViewController:UIViewController {

    var player —Variables for controlling AVAudioPlayer?//BGM
    var soundManager=SEManager() // Variables instantiated in SEManager
    // BGM playback method
    funcplay(soundName:String) {
        // Load sound file
        let soundPath=NSBundle.mainBundle().bundlePath.stringByAppendingPathComponent(soundName)
        // Pass the loaded file
        let url —NSURL?=NSURL.fileURLWithPath(soundPath)
        do{
            // Set the path to the mp3 file loaded into ↓player
            player=try AVAudioPlayer(contentsOfURL:url!)
        } catch_{
            player=nil
        }
        player?.numberOfLoops=-1// Loop BGM indefinitely
        player?prepareToPlay()// Immediately play audio.
        player?play()//Play sound
    }


    override func viewDidLoad(){
        super.viewDidLoad()

        //bgm
        // Do any additional setup after loading the view, typically from anib.
        Calling the //play method.The argument is the filename.
        play("bgm1.mp3")


        let screen = GameScene (size: CGSize (width: 750, height: 1334))
        let skView=self.view as!SKView
        scene.scaleMode=.AspectFit
        skView.presentScene(scene)
    }

    override func shouldAutorotate()->Bool{
        return true
    }

    override func supportedInterfaceOrients()->UIInterfaceOrientationMask{
        if UIDevice.currentDevice().userInterfaceIdiom==.Phone {
            return UIInterfaceOrientationMask.AllButUpsideDown
        } else{
            return UIInterfaceOrientationMask.All
        }
    }

    override funcdidReceiveMemoryWarning(){
        super.didReceiveMemoryWarning()
        // Release any cached data, images, etc that aren't in use.
    }

    override funcprefersStatusBarHidden() - >Bool{
        return true
    }
}

import SpriteKit
import AVFoundation

classGameScene:SKScene{
    // prepare a sprite for illustration
    let mySprite=SKSpriteNode(imageNamed: "omikuji.png")
    // prepare a sprite for buttons
    let btnSprite=SKSpriteNode(imageNamed: "button.png")
    // prepare labels for omikuji results
    let myLabel=SKLabelNode(fontNamed: "Verdana-bold")

    override func DidMoveToView (view:SKView) {



        // color the background
        self.backgroundColor=SKColor.whiteColor()
        // display an illustration
        mySprite.position=CGPoint (x:375, y:900)
        addChild (mySprite)
        // display a button
        btnSprite.position = CGPoint (x:375, y:200)
        self.addChild(btnSprite)
        // display omikuji result labels
        myLabel.text="???"
        myLabel.fontSize=65
        myLabel.fontColor=SKColor.blackColor()
        myLabel.position=CGPoint (x:375, y:500)
        self.addChild(myLabel)
    }
    // Touch Action
    override functouchesBegan(touches:Set<UITouch>, withEvent:UIEvent?) {
        for touch:AnyObject into touches {
            // Look at what's in the touched position.
            let location = touch.locationInNode(self)
            let touchNode=self.nodeAtPoint(location)
            // If it's a button,
            iftouchNode==btnSprite{

                // BGM does not stop when sound effects occur


                // the creation of sound effects data
                let mySoundAction: SKAction=SKAction.playSoundFileNamed("hit.wav", waitForCompletion:true")
                // playback action
                self.runAction (mySoundAction);

                // Mark ??? and then wag the omikuji
                myLabel.text="???"
                shakeOmikuji()
            }
        }
    }
    // omikuji-shaking process
    func shakeOmikuji(){

        // BGM sample 1 stopped playing
        // Now I want to switch background music to sample 2


        // [Turn on the action of wielding omikuji]
        // the action of tilting the omikuji slightly to the right
        let action1 = SKAction.rotateToAngle (-0.3, duration: 0.2)
        // the action of tilting the omikuji slightly to the left
        let action 2 = SKAction.rotateToAngle (0.3, duration: 0.2)
        // the action of turning over a lottery ticket
        let action 3 = SKAction.rotateToAngle (3.14, duration: 0.2)
        // Action 1, action 2, action 3 in the order specified
        let actionS = SKAction.sequence(
            [action1, action2, action1, action2, action1, action3])

        // Add an action to the omikuji and run kekka at the end.
        mySprite.runAction(actionS, completion:showOmikuji)
    }
    // The process of displaying results
    func showOmikuji(){
        varomikuji = ["Okichi", "Nakayoshi", "Kichi", "Kichi"]
        letter=Int(arc4 random_uniform(4))
        myLabel.text=omikuji[r]
    }

    override func update (currentTime:CFTimeInterval) {
    }
}