When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state. See screenshot
This will take you back to the 2018 online tax return.
Click on Tax Tools on the left side of the online program screen. Then click on Print Center. Then click on Print, save or preview this year's return. Choose the option Include government and TurboTax worksheets
The tax data file you downloaded that has a file extension of .tax2018 can only be opened by the TurboTax software for tax year 2018.