Hi,
Amend the Value of B2C Large Invoice to Zero in Table 9A of Form GSTR-1 and add that invoice in B2B Table 4A,4B,4C,6B,6C and by doing that you will have a difference in your GSTR 3B and GSTR1 of that month/Quarter but that is the only option by which it can be amended and in case of any notice in future you have to present this case by explaining this amended transaction.