class Program
    {
        static void Main(string[] args)
        {

            //Console.WriteLine("Hello World!");
            try
            {
                
                //using (var workbook = XLWorkbook.OpenFromTemplate(@"D:\aaa.xlsx"))
                using (var workbook = new ClosedXML.Excel.XLWorkbook(@"PATH_TO\aaa.xlsx"))
                {
                    //var worksheet = workbook.Worksheets.Add("DA01");

                    var worksheet = workbook.Worksheet("111");
                    worksheet.Cell("A6").Value = "Test";
                    workbook.Save();
                    //workbook.SaveAs(@"D:\aaa_saveas.xlsx");

                }

                System.Console.WriteLine("finished");
            }
            catch (System.Exception ex)
            {
                System.Console.WriteLine(ex.Message);
            }

            System.Console.ReadKey();

        }
    }