See the sample lines of code that you may try for your needs:
e.g
Sample code:
........
TxtSaveOptions options = new TxtSaveOptions(SaveFormat.CSV);
options.Separator = Convert.ToChar("|");
// Save the workbook in output CSV format.
workbook.Save(dirPath + "XLStocsv_Dummy.csv", options);
Hope, this helps a bit.