How to save excel file stored in project folder on local drive on button click in windows form C#

private void btnSample_Click(object sender, EventArgs e)
        {
            SaveFileDialog sfd = new SaveFileDialog();
            sfd.Filter = "Excel file |*.xls;*.xlsx;*.csv";
            if (sfd.ShowDialog() == DialogResult.OK)
            {
                const string MyFileName = "sample.csv";

                string execPath = Path.GetDirectoryName(Assembly.GetExecutingAssembly().CodeBase);
                var filePath = Path.Combine(execPath, MyFileName);

                Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application();
                Microsoft.Office.Interop.Excel.Workbook book = app.Workbooks.Open(filePath);

                book.SaveAs(sfd.FileName); //Save   
                book.Close();
            }
        }