What did you use for your 2017 return? If you prepared your 2017 return in Online TurboTax in a paid edition, the access to prior online returns should not be locked. If you prepared your 2017 return in desktop TurboTax (CD/download), prior online returns may or may not be locked, depending on other circumstances.
Even if they are locked, you may not have to pay to unlock them, depending on what you are using for 2018.
What are you using for 2018? Near your screen name above it's indicating that you are using the desktop Premier Edition for Windows. Is that correct? If you are using desktop Premier for 2018, that qualifies to unlock all prior online returns without additional payment. But the desktop software does not communicate that to your online account, so your locked online returns won't automatically know you have already bought a 2018 product. We can tell you how to do that by phoning Customer Support.
So please answer the above questions about what you used for 2017 and what you are using for 2018, and we can give you more info. If you are using desktop Premier (CD/download) for 2018, you shouldn't have to pay anything additional to get online returns, and we can tell you what to do.
I presume you also bought the 2017 desktop software (CD/download) since you need it to prepare the 2017 return. Once TurboTax Support unlocks your prior online returns, you can download the *.tax2016 data file and transfer it into a new 2017 desktop return. The 2017 return cannot be efiled. It has to be printed, signed, dated, and mailed. If you have both Federal and state returns, you mail them separately to the respective tax agencies.
Once you finish the 2017 return, you can transfer the *.tax2017 data file into a new 2018 return in the 2018 software.
See my comment above about preparing the 2017 and 2018 returns in the desktop software. You will need two products: 2017 software and 2018 software. See the additional info above.
Access to prior online returns likely expired when you didn't use a 2017 paid version last year; i.e., since you didn't prepare a 2017 return.
The way to restore access to locked Online returns is to pay for a 2018 product--either 2018 Online TurboTax in the same account, or 2018 desktop software (CD/download). If you purchased 2018 desktop software, then that qualifies to unlock the prior returns. See the info below on how to speak to TurboTax Support so you can tell them you purchased 2018 software and ask them to unlock your prior online returns.
You can use the form at the link below to schedule a call back, or it may provide a number. Hours are 5AM-9PM Pacific (8AM-12 Midnight Eastern) 7 days/week.
Where the form asks what product you are using, be sure in the dropdown menu to indicate "CD/download" and the proper operating system, then indicate which Edition.