using System;

public class Program

{

    public static void Main()

    {

        var en = new System.Globalization.CultureInfo("en");

        var reaData = "21.04.2022";

        var reaFormat="dd.MM.yyyy";

        var formatOut="yyyy-MM-dd";

        DateTime dateValue;

        if(!DateTime.TryParseExact(reaData,reaFormat,en,System.Globalization.DateTimeStyles.None,out  dateValue)){

        Console.WriteLine("Failed");

        }else

        Console.WriteLine(dateValue.ToString(formatOut));

    }

}