How can I connect my Windows application with a program that runs on localhost

I'm developing an application that is for the Windows store. The application has buttons that send you to a couple of domains.

private IDictionary<string, string> environments = new Dictionary<string, string>(){
            {"DEMO", "https://somedomain.com"},
        };
        
public MainPage()
        {
            this.InitializeComponent();
        }

        
public void navigateToDemo(object sender, RoutedEventArgs e)
        {
            Trace.WriteLine( this.Frame.Navigate(typeof(AppView), environments["DEMO"]) );
        }

I want to test some changes of one of the pages that the user can be sent to, but I want to test the changes instantly, not having to deploy a whole new version just to see some small change.

When I change the URL to the localhost, the page doesn't load anymore...

How can I do this?