start of the week C#

     
  public static class DateTimeExtensions
    {
        public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
        {
            int diff = dt.DayOfWeek - startOfWeek;
            if (diff < 0)
            {
                diff += 7;
            }

            return dt.AddDays(-1 * diff).Date;
        }
    }
    

Usage:

     
dateFrom.Value = DateTime.Now.StartOfWeek(DayOfWeek.Sunday);