The online version of TurboTax can only be used for completing a current tax filing year tax return, and for 2019 that has been shut down since Oct 15, 2020. To complete a prior year tax return you must use the CD version of TurboTax 2018 that you physically install on your computer.
You can purchase TurboTax 2018 at https://turbotax.intuit.com/personal-taxes/past-years-products/ Just click on the "File 2018 Taxes" link and go from there to purchase the CD version of whatever flavor you need. After you pay for it, you will be able ot download the installation file so you don't have to wait for the CD to arrive in the mail.
Once downloaded, double-click the downloaded file to install it. Once installed, click the TurboTax 2018 icon on your desktop to get started.
Take note that a prior year tax return can not be e-filed. The IRS says so. You will have to print, sign and mail it to the IRS. When you select the "Print and Mail" option an instruction sheet will be printed with it. That instruction sheet will tell you what forms you need to include with your mailing, along with the address to mail it to.
If you will also be completing a state return, a physically separate instruction sheet is printed for the state return. The state return will ***NOT*** be mailed to the same address as your federal return. So pay attention to detail.
