How to wait for on onNotificationOpen if notification is tapped

Hello,

I’m facing logical problem with FCM integration.

As i’m trying to open different page when particular notification is tapped.

But when i open app using taping on notification, my page redirects correctly but then it will again redirect to Intro or Video page as given in platform.ready below.

What I want is, if i open the app using notification then other code will not be executed.

Can anyone please advice. My code of app.component.ts is below.

changepage: any = false;
    this.platform.ready().then(() => {
        // Okay, so the platform is ready and our plugins are available.
        // Here you can do any higher level native things you might need.
        this.statusBar.styleDefault();
        this.splashScreen.hide();
        this.fcm.onNotificationOpen().subscribe(res=>{
            **//Below is flag to change navigation of page. If notification is tapped then it should not execute condition( if(!this.changepage)) below.**
            this.changepage = true;
            alert(JSON.stringify(res));
            if(res.page=="lostfound")
            {
                this.nav.setRoot(Tagmap,{name: res.name,lattitude:res.lat,longtitude:res.lon});
            }
        }, (error)=>{
            alert(error);
        },
        ()=>{
            alert("complete");
        });
        **// this will alway given false as below statement isn't wait for this.fcm.onNotificationOpen() to execute.**
        alert(this.changepage);
        if(!this.changepage)
        {
            alert("changepage");
            this.ls.getUserid().then((user_id)=> {
                if(user_id == null){
                    this.rootPage = Intro;
                } 
                if(user_id != null) {
                     this.rootPage = VideoPage;
                }
            });
       }
    });

Please advise.

-Naitik