After you file

You can add the slips to your existing return.

This TurboTax FAQ tells you how to do this using ReFile: https://turbotax.community.intuit.ca/turbotax-support/en-ca/help-article/accounting-bookkeeping/file...

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...