Have you used TurboTax Online Version or TurboTax Desktop Version? You can make changes to a filed tax return by filing a T1-adjustment. The CRA requires that you wait until you’ve received your Notice of Assessment (NOA) before filing an adjustment.  In many cases, the CRA will catch the mismatch and automatically adjust your return for you.

For step-by-step instructions, please follow this TurboTax article:  I've filed my tax return. Can I still make changes?

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