If a return has been filed, how can it be revised if some changes are required to be made?

In GST since the returns are built from details of
individual transactions, there is no requirement for having
a revised return. Any need to revise a return may arise
due to the need to change a set of invoices or debit/ credit
notes. Instead of revising the return already submitted, the
system will allow changing the details of those transactions
(invoices or debit/credit notes) that are required to be
amended. They can be amended in any of the future GSTR-
1/2 in the tables specifically provided for the purposes of
amending previously declared details.