How do I access my previous year tax return. I haven't filed since 2017 and need to file both 2018 and 2019 but cannot figure out how to do it

Did you use this TurboTax website to purchase the 2018 and 2019 desktop editions - https://turbotax.intuit.com/personal-taxes/past-years-products/

If so, go to your download account and sign in with the exact same User ID used to purchase the software - https://shopping.turbotax.intuit.com/unified/downloads?route=myaccounts

The 2018 and 2019 tax returns can only be printed and mailed, they cannot be e-filed.

For your prior year tax returns completed using the TurboTax online editions - 

To access your current or prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/

Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show.  Click on the Year and Click on Download/print return (PDF) or Download .tax file