Online TurboTax can only prepare a 2019 return at this point in time. For a 2018 return, you'll need to use 2018 desktop software (CD/download).
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
Or 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 desktop software. If you already paid for your product previously, TurboTax Support should furnish you the software.
The 2018 return cannot be efiled. It will need to be printed, signed, dated, and mailed. It is recommended to mail by a method that has tracking such as certified return receipt, priority mail, etc.
If you have both Federal and state returns, you need to mail each one separately to its respective tax agency.
If you are due a Federal refund, it takes about 6 weeks for the IRS to process a mailed return.
