If you make a mistake on your tax return, you can make adjustments to the same tax return in the following 3 ways: Online: You can go to “My Account” to view your tax return and through “Change my return” request changes to the tax return. ReFILE: If you filed the tax return electronically, you can use ReFILE to send adjustments to tax returns for 2018 and later years. You’ll also have to keep supporting documents with you, in case the CRA wants to see them. By mail: You can make adjustments to a tax return by mail, however, the processing can take longer. You should fill out Form T1-ADJ, T1 Adjustment Request and attach all the supporting documents and send the change request to the CRA separate from your current year’s tax return if you are requesting a change to a previous year’s return.