ControlMT4.cs

using System.Collections.Generic;
using System.Linq;

// https://www.nuget.org/packages/TestStack.White
using TestStack.White;
using TestStack.White.UIItems;
using TestStack.White.UIItems.Finders;

namespace MTBacktester
{
    class Program
    {
        static void Main(string[] args)
        {
            Application app = Application.AttachOrLaunch(new System.Diagnostics.ProcessStartInfo(@"C:\Program Files (x86)\MetaTrader 4\terminal.exe"));
            var windows = app.GetWindows();
                       
            var criteria = SearchCriteria.ByText("Expert properties").AndControlType(typeof(Button), WindowsFramework.Win32);

            windows.Last() // main window
                .Get<Button>(criteria) // "Expert Properties" button
                .Click(); 

            windows.Last() // inputs window
                .Get<Button>(SearchCriteria.ByText("Load"))
                .Click();

            windows.Last() // file choosing dialog
                .Get<Button>(SearchCriteria.ByText("Cancel"))
                .Click();
        }
    }
}