Search for “loss carryback” and add the Request For Loss Carryback section to your return. You can designate net and non-capital losses to carry back to prior years in this section. You’ll need to figure out your maximum carry-backs (by reviewing your prior year returns) before completing this section.
Adding an amount to the Request For Loss Carryback section will not change your tax payable (refund or balance) for the current year. When the CRA receives your current year return they will automatically reassess your prior year return and send you a refund for that year.