After upgrading the 2018 return, it is the paying by credit/debit card that unlocks prior returns. Did you actually pay? The 2018 and 2017 returns must be in the same account. The minimum upgrade is PLUS at 19.99.
However, you have another problem to resolve first. You appear to have upgraded to Deluxe, (at least that is what is displayed beneath your question above.) If so, Deluxe is 59.99 for a Federal return, and 44.99 for a state return, if applicable. Whether or not you can downgrade it yourself, or whether you will have to phone Customer Support depends on whether or not you have already filed your 2018 return. Which of the following 2 choices is your scenario?
If you have not yet filed your 2018 return, we can tell you how you may be able to downgrade to Free Edition using "Clear and Start Over", then upgrade to PLUS for 19.99 and pay by credit/debit card.
If you have already filed the 2018 return, however, you can phone TurboTax Support and tell them you had already filed 2018, then upgraded too far by accident after filing, and ask them to unlock the 2017 return for you. They may not even charge you.
Hours are 5AM-5PM Pacific (8AM-8PM Eastern).
FAQ: What is the TurboTax phone number?
For the sake of completeness, 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.