Purchase Return invoice not mention in GSTR 1

Krishan Kumar Jha (28 Points)

02 July 2021  
we supply goods to our customer and charge GST and the same paid
But customer returns the good and issues purchase return invoice GST charged
they are not mention purchase return invoice in GSTR 1
they say that we had reversed the ITC against delivery note of purchase return in GSR- 3B
How I claim ITC against purchase return invoice
please help me