Amendments can be made to a submitted tax return form depending on when the amendments are/ can be submitted:

Submitting amendment before tax deadline: Submit a letter detailing the mistake(s) made with supporting documents (receipts, invoices, statement, etc) to the responsible branch that handles your tax file.

Submitting amendment within 6 months from tax deadline: Make a self-amendment by submitting an Amended Return Form (ARF) to the responsible branch that handles your tax file. Only taxpayers who submitted their tax returns on time can make a self-amendment.