How to get a method and invoke by reflection

this is a class called "App" and there is a private method in this class

private void Application_Startup(object sender, StartupEventArgs e)
    {}

in another program I want to reflect the "App" class and invoke Application_Startup method. but it is private method, how can I do ? thanks.

Assembly winForm = Assembly.LoadFile("....");
            App obj = (App)winForm.CreateInstance("App");