Have you located the 2017 return, but access is locked, and it's asking you to pay? We can tell you all the steps, but you have another problem to work through first.
You appear to be in an edition already higher than PLUS. Underneath your question it says you are using DELUXE. Deluxe is 59.99 for a Federal return and 44.99 for any state return, if applicable. The minimum to unlock a return is to upgrade a 2018 Free Edition return to PLUS at 19.99.
How did you end up in Deluxe? Is that what you used to file your 2018 return, or did you upgrade too far after filing in an attempt to get the 2017 return? Are the 2017 and 2018 returns in the SAME account?
If you have already filed the 2018 return, you won't be able to downgrade it yourself. We can tell you how to contact Support to remedy that and unlock the 2017 return for you. They may not even charge you.
If you haven't yet filed the 2018 return, we can tell you how to downgrade and end up in PLUS for 19.99.
There's also a free option if a 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.