NO, you cannot add 2018 W2's to your 2019 return. You would need to file a 2018 return & enter your income.
You cannot file a previous years return with the Online version, the Online version is only to file the current years tax return.
Prior year returns cannot be e-filed with TurboTax. To file your 2018 return with TurboTax you will need to use the 2018 Download software (or go to the IRS website for prior year forms). To purchase the software from TurboTax go to the following website.
https://turbotax.intuit.com/personal-taxes/past-years-products/
