Amendment in Outward Supply invoice pertaining to year 2018-19

Amendment to be made : Wrong GSTIN was mentioned in GSTR 1. Due to this error, customer of our client could not avail ITC for which he is legally entitled.

I would like to make above amendment in an invoice for the year 2018-19. The due date to amend details for given year has expired. (20 October 2019)

Sadly, the error was not realised before September 2019. But, amendment of invoice is necessary.Is there any possibility to amend the invoice through by posting a query on GST portal?