How can I make a property change from a different xaml Page with the use of MVVM?

I'm newbie in MVVM . I have two xaml pages. the second one cannot be accessed ( Locked ) unless the button from the first page (Introduction page) has been clicked. How can I do that?

The lock page has this code.

<Frame Grid.Row="0" Grid.Column="1" BackgroundColor="LightGray" IsVisible="{Binding LockPage}">
            <Frame.GestureRecognizers>
                <TapGestureRecognizer Tapped="Tap_Lock" />
            </Frame.GestureRecognizers>
            <Label Text="Locked"/>
        </Frame>

The Introduction page has this code.

<StackLayout>
    <Label Text="This is only a simple Introduction Text."/>
    <Label Text=""/>
    <Button Text="Lets Go!!" Command="{Binding UnlockPageCommand}" Clicked="Tap_Next"/>

This is the the class LockModule.cs

public class LockModule : INotifyPropertyChanged

{

public LockModule()
{
    UnlockPageCommand = new Command(UnlockPage);
}

bool lockPage = true;
public event PropertyChangedEventHandler PropertyChanged;

void OnPropertyChanged(string lockpage)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(lockpage));
}

public bool LockPage
{
    get { return lockPage; }
    set
    {
            lockPage = value;

        OnPropertyChanged(nameof(LockPage));
    }
}

public Command UnlockPageCommand { get; }

void UnlockPage()
{
    if (lockPage == true)
    {
        lockPage = false;
    }
    else
    {
        lockPage = true;
    }
    OnPropertyChanged(nameof(LockPage));
}

}

and it's not working