If you filed using TurboTax Online you will need to sign into your TurboTax Online account using the same credentials as you used to complete your return. Here is the link to the TurboTax 2021 sign in here- https://ww1.2021.turbotaxonline.intuit.ca/signin?_swlg=en.
Here is the video to watch to see the steps to view your past returns.