If you are seeking to prepare and file a PRIOR YEAR tax return, here is the method still available:
Every year. the online system closes on the last legal day for filing, which is October 15th. The IRS closes eFile on that date.
To use TurboTax to enter and submit a prior year return, you must choose to purchase the prior year's [2017, for example] desktop software and install it. You can purchase it from TurboTax but find it at lower cost from Amazon and other reputable dealers. Remember to immediately run online update to the software that you have had to install.
Note that the IRS also shuts down eFile for that prior year at the same time, so you will have to print and mail the return.
If you started but never finished the 2017 return but did at least start it and possibly made entries, go here:
https://ttlc.intuit.com/questions/4501187-where-can-i-find-my-prior-year-2017-return
Then: Read this:
https://ttlc.intuit.com/questions/1900990-how-do-i-prepare-a-prior-year-tax-return