FORM GSTR-6A contains the details of inward supplies received by Input Service Distributors from registered taxable persons and debit/credit notes received. This statement is auto populated from FORM GSTR-1 and FORM GSTR-5 filed by other assesses bearing the same PAN as the Input Service Distributor.
(ICAI FAQ PUBLICATIONS 06-09-2017 RETURNS : FAQ NO. 21)