How to find my elderly father's return, which I do every year? Turbo tax goes directly to mine with no option to choose another (my dad's).

No.  Online is only good for 1 return per account.  But you can use the same email address for 5 accounts.   How to start another return in the Online version

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-online/00/25596

If you did 2 returns in the same account the second one done will overwrite the first one.  See if you have another account.  

How to view all your accounts
https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/many-intuit-accounts-turbotax/L9aVfKS1Z_US_en_US?uid=ll5g6zcx

It's common to end up with multiple accounts. First LOG OUT of whatever TurboTax account you're logged into right now. Then use this TurboTax account recovery website to get a list of user ID's for an email address. Run the tool against any email addresses you may have used
https://myturbotax.intuit.com/account-recovery/

If you used the Desktop CD/Download program then the only copy is on your computer and not saved or stored online.

You can also request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript

The Desktop CD/Download program can do unlimited returns and efile 5.  You can buy the Desktop CD/Download program at

TurboTax® 2021-2022 CD/Download Tax Software, Compare Desktop Tax Preparation