Purchase invoice missing in gstr2a

We are 100% export unit at the time of refund the department says that whatever bill reflecting in GSTR 2A you will get refund for that only....for other what I can do.

I have followed vendors but they did nothing or told that there is no option for previous month now

Is there any way right now where I can enter my missing invoice or any specific way whcih vendor should follow to correct his mistake.

Please advise.

Thanks in advance

Amit