Dear Namrata
The custom Act ,1962 provides for removal of goods from Custom station to a warehouse without payment of duty.The said Act has been amended to include "warehous" in the Defination of "Custom Area"
So the goods being transferred or deposited in custom bonded warehouse ,the Importer is not required pay duty & IGST on same .
As per Circular 3/1/2018 GST : the Importer file into-bond bill of entry & stores the goods into custom bonded warehouse & thereafter supplies such goods to some other person who then file Ex-bomd bill of entry for clearing the said goods from Custom bonded warehouse for home consumption then IGST & duty is leviable.
And if we read the sub Section (2) of Section 7 of IGST Act , it's not supply till the imported goods cross the Custom Frontiers of India. And as per Circular IGST is levied & collected at the time of clearances of goods from warehouse for home consumption.
Since the goods were directly exported from custom bonded warehouse & not brought for consumption in India , not crossing the custom frontier. So it's not an supply , it can be cover under Merchant Export
SO ITS MERCHANT Export & cover under Schedule III , you need to report such in Table 8 of GSTR 1. & In GSTR 3B it can be reported under Table 3.1(e)
Final conclusion : Neither the supply goods nor supply of Services. So No Duty & IGST is applicable.