ADDENDUM:
If your 2018 tax data file has a state return in it, then you will need to download the state software into your TurboTax program first before opening the tax data file, or it will give you an error notice.
If it gives you such an error, you may have to minimally start a new fake 2018 return in the 2018 software to download the state program. You can delete that fake return later. Be sure you delete the right one and not your actual tax data file. So be sure to name it something like "fake" or "test" or something so you'll know.
