Hi Vincent,
Please feel free to contact us if you have any other question.
Sincerely,
Betsy
E-iceblue support team
var workbook = new Workbook();
var worksheet = workbook.Worksheets.First();
worksheet.Range["B2"].Value2 = new DateTime(2017, 01, 30);
worksheet.Range["B2"].NumberFormat = "m/d/yyyy";
workbook.SaveToFile(Chemin + "Sample - Out.xlsx", ExcelVersion.Version2016);