Did you already start a 2018 return online prior to the 2018 online shutdown, and want to finish that one without starting over? If so, you can download the *.tax2018 data file from your account and finish it in the 2018 desktop software. If you already paid for your 2018 product previously, TurboTax Support should furnish you the software.
If you had not paid for a 2018 product, you can purchase 2018 desktop software as a download at this page and install it on your computer:
https://turbotax.intuit.com/personal-taxes/past-years-products/
Minimum system requirements for Windows version:
https://ttlc.intuit.com/questions/1901571-minimum-system-requirements-for-turbotax-windows-software
Minimum system requirements for Mac version:
https://ttlc.intuit.com/questions/1899173-minimum-system-requirements-for-turbotax-mac-software
The 2018 return cannot be efiled. It will need to be printed, signed, dated, and mailed. It's a good idea to mail by a method that has tracking, such as certified mail, priority mail, etc.
If you have both Federal and state returns, you need to mail each one separately to its respective tax agency.
OR another option is to download the 2018 forms and instructions for free from the IRS website and fill them out manually.
https://www.irs.gov/forms-pubs/prior-year
