How can I access last year's return, which was filed with TurboTax under someone else's account, and save it in my account?

[TurboTax-Marisa]

TurboTax returns can't be moved from one account to another, but if it's your prior-year return, you could ask the owner of the account to provide you with a copy of your return. Here's how they can print it: https://turbotax.community.intuit.ca/replies/2648070