TurboTax 2019 online editions - https://turbotax.intuit.com/personal-taxes/online/

TurboTax 2019 desktop CD/Download editions - https://turbotax.intuit.com/personal-taxes/cd-download/

To complete and file a prior year, 2016 thru 2018, tax return using TurboTax you would need to purchase, download and install on a personal computer one of the desktop editions for each tax year required from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/

A prior year tax return can only be printed and mailed, it cannot be e-filed.

You can do 2019 online here,  https://turbotax.intuit.com/personal-taxes/online/

Or buy the 2019 Desktop program here,  https://turbotax.intuit.com/personal-taxes/cd-download/

You can only buy the prior year desktop programs.  You have to buy a different program for each year.  You  can buy 2017 & 2018 here,

https://turbotax.intuit.com/personal-taxes/past-years-products/ 

If you buy the Desktop program you can buy any version.  All the Desktop program have the same forms so you can buy a lower version like Deluxe.