Sorry, You can not do 2018 and prior using Turbo Tax. They only sell the last 3 years. You might want to go to a local accountant or tax place if you have a complicated return. For simple returns you can fill out the forms by hand. And it is too late to get any refunds.
Or If you have a simple return You can fill out the blank forms for free.
Here is the IRS 2018 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2018.pdf
And instructions https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-prior/i1040tt--2018.pdf
IRS 2018 Schedules 1 thru 6 (only if needed)
https://www.irs.gov/pub/irs-prior/f1040s1--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s2--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s3--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s4--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s5--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s6--2018.pdf
Don’t forget your state. And you will have to print and mail your returns. So be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
Also keep in mind, that if you have a refund due after completing your 2018 tax return, you will not receive it. The IRS has a 3-year statute of limitations on paying refunds not claimed within three years of the due date of the tax return. Since the 2018 return was due by Apr 18, 2019, you are well past 3 years.
However, on the other side of that coin, if you owe taxes you are still required to pay them, plus interest that started accumulating on the Apr 18, 2019 due date.