Алек Оним

public System.Windows.Forms.WebBrowser webBrowser = new System.Windows.Forms.WebBrowser();

public MainWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            for (i = 0; i <= 10; i++)
            {
                webBrowser.Navigate(new Uri("https://account.mojang.com/migrate"));
                webBrowser.Navigated+=DoWork;
            }
        }

        private void DoWork(object sender, WebBrowserNavigatedEventArgs e)
        {
            Random rand_date = new Random();
            foreach (HtmlElement element1 in webBrowser.Document.All)
            {
                if (element1.GetAttribute("name") == "migrationRequest.dayOfBirth")
                {
                    element1.Children[rand_date.Next(1, element1.Children.Count)].SetAttribute("selected", "true");
                }
            }
        }