To add this credit to your previous year's returns, you would have to adjust them using either ReFIle or another method as per the CRA. 

This TurboTax Canada FAQ tells you how to use ReFile: https://turbotax.community.intuit.ca/turbotax-support/en-ca/help-article/accounting-bookkeeping/file... ReFile is not avaialble for TurboTax Online 2021 or earlier, or TurboTax Desktop 2019 or earlier.

This Canada Revenue Agency (CRA) web page lists other ways to can adjust your return: https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/change...