First, convert it to a DateTime:
DateTime dt;
if (!DateTime.TryParseExact(@"17-11-2017 13:59:00", "dd-MM-yyyy HH:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.None, out dt))
{
return;
}
(if you have it in a DateTime, you can skip this part)
Then use ToString to format it for presentation:
string formatted = dt.ToString(@"yyyy-MM-dd HH:mm:ss.fff");