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,
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.