It appears from your post that you are currently in the Deluxe edition of TurboTax Online.
You'll need to go ahead and make payment for the Deluxe program (or PLUS if you want to downgrade to that first) in order to unlock your prior-year returns. See instructions below for making payment to unlock your prior year returns.
https://ttlc.intuit.com/replies/5574744
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
