Missing bills in gstr-1

Hello Sir,

I would like to inform you that I have failed to put 2 Sales Bills of the months of October'18 & November'18 in GSTR-1, which I filled in December Quarter. I have successfully filed the GSTR-3 for the months of October & November with these bill details. 

How can I add the bills so the buyer can get the ITC for the same. Please advice.