Export.cs

public async Task<IActionResult> Export()
        {
            string sWebRootFolder = _hostingEnvironment.WebRootPath;
            string sFileName = @"Employees.xlsx";
            string URL = string.Format("{0}://{1}/{2}", Request.Scheme, Request.Host, sFileName);
            FileInfo file = new FileInfo(Path.Combine(sWebRootFolder, sFileName));
            var memory = new MemoryStream();
            using (var fs = new FileStream(Path.Combine(sWebRootFolder, sFileName), FileMode.Create, FileAccess.Write))
            {
                IWorkbook workbook;
                workbook = new XSSFWorkbook();
                ISheet excelSheet = workbook.CreateSheet("employee");
                IRow row = excelSheet.CreateRow(0);

                row.CreateCell(0).SetCellValue("EmployeeId");
                row.CreateCell(1).SetCellValue("EmployeeName");
                row.CreateCell(2).SetCellValue("Age");
                row.CreateCell(3).SetCellValue("Sex");
                row.CreateCell(4).SetCellValue("Designation");

                row = excelSheet.CreateRow(1);
                row.CreateCell(0).SetCellValue(1);
                row.CreateCell(1).SetCellValue("Jack Supreu");
                row.CreateCell(2).SetCellValue(45);
                row.CreateCell(3).SetCellValue("Male");
                row.CreateCell(4).SetCellValue("Solution Architect");

                row = excelSheet.CreateRow(2);
                row.CreateCell(0).SetCellValue(2);
                row.CreateCell(1).SetCellValue("Steve khan");
                row.CreateCell(2).SetCellValue(33);
                row.CreateCell(3).SetCellValue("Male");
                row.CreateCell(4).SetCellValue("Software Engineer");

                row = excelSheet.CreateRow(3);
                row.CreateCell(0).SetCellValue(3);
                row.CreateCell(1).SetCellValue("Romi gill");
                row.CreateCell(2).SetCellValue(25);
                row.CreateCell(3).SetCellValue("FeMale");
                row.CreateCell(4).SetCellValue("Junior Consultant");

                row = excelSheet.CreateRow(4);
                row.CreateCell(0).SetCellValue(4);
                row.CreateCell(1).SetCellValue("Hider Ali");
                row.CreateCell(2).SetCellValue(34);
                row.CreateCell(3).SetCellValue("Male");
                row.CreateCell(4).SetCellValue("Accountant");

                row = excelSheet.CreateRow(5);
                row.CreateCell(0).SetCellValue(5);
                row.CreateCell(1).SetCellValue("Mathew");
                row.CreateCell(2).SetCellValue(48);
                row.CreateCell(3).SetCellValue("Male");
                row.CreateCell(4).SetCellValue("Human Resource");

                workbook.Write(fs);
            }
            using (var stream = new FileStream(Path.Combine(sWebRootFolder, sFileName), FileMode.Open))
            {
                await stream.CopyToAsync(memory);
            }
            memory.Position = 0;
            return File(memory, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", sFileName);
        }