Not able to covert excel date values into IST format

In my client application there is one functionality download the excel for the particular records,  there is four date values are used Identified On, Due On, Completed On and Approved On, These all values are  currently show in UTC format and I have one API which are using the same fields to publish data, So API  I added conversion logic so its is working fine and show properly in IST format but in excel exporter  functionality the logic is not working. The date are totally showing different in API Response and the Excel. Tried the parseDateTime function and also checked with adding 5.30 hours for converting the date values but not working, Please provide the possible solution for these. Thanks in Advance !  
1 answers

Hi, are you sure the excel date are in epoch format? Excel uses the 1900 or 1904 date system. In the past I had to convert the before formatting.