Difference in books and gst returns fy 19-20

dear professional colleagues some gstr 1 and 3b for different month are mismatch from books of account in fy 19-20 and also some invoice for fy 19-20 are not recorded in books and also not considered in gst return till now.my questions are
how can I correct this mismatch.
treatment of unrecorded invoices in books and gst.

thanks in advance