Normally it requires a 2019 purchase. You can phone support as DoninGA mentioned and ask them if they will unlock the 2017 return for you based on your 2018 product purchase, but they may not. Or they may be generous.
In any case, the "Add a State" method you mentioned to reopen a return does not apply at this point in time for your particular situation for a 2017 return.
Beginning tomorrow December 4, here are the expected full instructions (since 2019 online TurboTax hasn't opened yet, no one can actually test yet). But in any case, you can't use them until tomorrow (December 4) when Online TurboTax for 2019 is expected to open. But if they are the same as last year, then here's how:
- Start a 2019 Free Edition return in the SAME account as the locked 2016 return.
- After some preliminary screens, you'll arrive at the MY INFO section.
- See if there is an Upgrade link in the left menu column. If not, you'll need to enter some info into the MY INFO screens until you see an Upgrade link either appear in the left menu column. If not, then at the end of the MY INFO section, you should be able to Upgrade.
- Then click on Upgrade and choose PLUS. Do NOT upgrade any beyond PLUS, or you'll have problems.
- Once you are in PLUS, then you need to pay by credit/debit card.
- In the left menu column click on TAX TOOLS, then PRINT CENTER.
- At the Print Center choose to "Print, save, view THIS YEAR's return." (Yes, you say "this year's" because you are paying for the 2019 return to unlock the 2017 return.) You don't actually have to print it.
- It will ask you to pay. If the Order Summary appears OK, then choose PAY NOW.
- You can pay by credit card or debit card (even though it only says "credit.")
NOTE: If it should offer you the choice of paying later out of the Federal refund, that cannot be done for this purpose. You have to choose PAY NOW.
There's also a free option if a 2017 return transcript will suit your purpose. You may be able to immediately download one at the IRS website if you qualify to open an IRS account there. Otherwise, to order a transcript to come by postal mail takes 5-10 calendar days.
http://www.irs.gov/Individuals/Get-Transcript
