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Depending on the year of the return you want to adjust, you might be able to correct, using your tax software, like TurboTax, and then remit using the ReFILE option. You can make changes to your current and previous 2 tax years through Re-FILE using the same software you used to file originally.
You can also make this amendment through your CRA online account, log in, click on change my return, select the tax year of the return to change, select the line you need to change, add your figures, confirm and submit.
You can also submit a paper adjustment by completing a T1 adjustment form found on the Canada Revenue Agency website. Please refer to this link Click Here
For more information, visit TurboTax FAQ