QRMP GSTR1 PROBLEM

According to me there is no clarifications till if data upload by IFF for jan and Feb that it should to auto fill in Gstr1 of March but it is not reflecting in March Gstr1. in senerio according to me you need to upload the detail only March in Gstr1

If IFF is already filed for Jan and Feb 21 than no need to upload that invoices again.
You have to upload only March month's invoices.

This Quarter it's not auto reflecting in 3rd months return,...but from next quarter and onward, first and second month's data will be auto populate in third month's GSTR 1

No need to upload the data again, since you have already uploaded. Just file your GSTR-1 by uploading details of March 2021 and showing your B2C supplies and HSN Summary. You can also raise a query on GST grievance portal