Try this ,
Var1 =
DateTime.FromOADate(yourExcelDate).ToString(“dd/MM/yyyy HH:mm:ss”)
The above will give you the output as string type so use it in assign activity with a string type variable on the left side.
For DateTime variable use,
DateTimeVar=
DateTime.ParseExact(var1, “dd/MM/yyyy HH:mm:ss”, CultureInfo.InvariantCulture)
Hope this helps .