how to overwrite on an existing template in my project, i am using epplus

Question

This is my code, it does not give me an error, but when I download the file, it eliminates the design of my template, how can I solve it?

        try
        {

          
            var oor_data_response = oDownloadReports.DownloadReports(1);

            var row = 3;

            string fullFilePath = Path.Combine((System.IO.Directory.GetCurrentDirectory()).Split(new string[] { "/bin/" },
                        StringSplitOptions.None)[0], "Layouts", "OOR_Report.xlsx");


           

                FileInfo file = new FileInfo(fullFilePath);

                using (ExcelPackage package = new ExcelPackage(file))
                {
                   
                    ExcelWorksheet worksheet = package.Workbook.Worksheets[1];

                    foreach (var items in oor_data_response)
                    {

                        worksheet.Cells[row, 1].Value = items.PART;
                        row++;
                    }


                    

                   
                    SaveFileDialog saveFileDialog1 = new SaveFileDialog();
                    //saveFileDialog1.Title = "Save Excel sheet";
                    saveFileDialog1.Filter = "Excel files|*.xlsx|All files|*.*";
                    saveFileDialog1.FileName = "Rpt_OOR_" + DateTime.Now.ToString("dd-MM-yyyy") + ".xlsx";


                    if (saveFileDialog1.ShowDialog() == DialogResult.OK)
                    {

                        

                        package.SaveAs(file);
                        MessageBox.Show("Export Successfully", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }

                }

           




        }
        catch (Exception ex)
        {

            MessageBox.Show(ex.Message.ToString(), "NPRC Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }