While filing the tax returns and string of GSTR forms, we tend to make wrong entries, include the wrong ones and omit the necessary items. However, it is possible to make GSTR-1 amendments but these cannot be made in all the cases and have their own limitations. Here are few things that an Individual should know before he is filing the form.
Filing Period –Once the amendment is made, the period of filing the return should be the one in which the amendment has been made. For instance, if the necessary amendments are made by the tax payer in the month of July then the filing period should be July for the monthly returns, it should be July-September.
Amendments possible at Invoice Level
At the invoice level, the tax payer have following choices:-
B2C large amendments
B2B amendments
Credit Debit Note Unregistered amendment
Credit Debit Note Registered Amendments
Export Invoice Amendments
Details that can be amended
The authorities offer the flexibility to make amends in some of the details of the GSTR-1 which have been filled in wrong. These details are:
Customer GSTIN
Export Invoices
Amending the tax invoice into bill of supply
Credit Debit Note
Shipping Bill Date/Bill of Export Date cannot be amended.
It is not possible to change the receiver/customer GSTIN but an individual can amend & link any other invoice for the same GSTIN
In case the receiver of the goods has already accepted or modified the invoices, the taxpayer cannot amend those invoices.
Various details such as reverse charge, customer HSTIN and place of supply are based on the Invoice which it is linked to. Therefore, both the details should match.

GSTR-1
Summary level amendments in GSTR-1
Other than Invoice level amendments, it is also possible to make the changes at the summary level. Here are the amendments that can be made at the summary level.
Advances Received (Tax Liability) Amendments
B2C Others Amendments
Adjustment of Advances Amendments
Details that cannot be amended in GSTR-1
Place of Supply
Nil rated and the HSN Summary of the Outward Supplies
Process to modify GSTR-1
On its official website under the FAQ section of user guide on GSTR-1, the authorities mention that to delete or modify the invoices one cane EDIT/DELETE button. Since the uploaded details are in a draft version, they can be changed until GSTR-1 is submitted.
Also, these changes can be made any number of times until the submission of GSTR-1 of that tax period.
It is not uncommon to make mistakes while filing the GSTR-1 but the limitations must be kept in mind because not all the details can be amended. In case you are filing the GSTR-1 for the first time, it would be advisable to take an expert assistance rather than getting trapped into the complex process.