The taxpayer once submits the return cannot change the value of Outward supplies. The value of outward supplies gets locked and any corrections or changes intended to be made has to be done while filing the GSTR-1
Since, you have filed GSTR 1 with correct information, no changes required in GSTR 1. However, you have do corrections in GSTR 3B of next month. so that you can reconcile GSTR 3B of consolidated period