You can no longer use TurboTax Online to file for 2018. TurboTax Online is only for the current tax year, which is now 2019. To file for 2018 you have to use the CD or download TurboTax software for 2018. You can purchase a download at the following link.
You might get a better price from a reputable online seller that still has TurboTax for 2018 in stock.
Tax returns for past years cannot be e-filed. You will have to print your 2018 tax return, sign it, and file it by mail.
I downloaded the Turbo software. It keeps asking me to find my 2018 tax return to admen, but I need to start my filing. How can I get past the admen to START?
Did you download and install the TurboTax software for 2018 from this TurboTax website - https://turbotax.intuit.com/personal-taxes/past-years-products/
If so, after you installed and started the TurboTax program it asks you if you want to start a new tax return. Or you can start a new 2018 tax return by clicking on the File menu on the top left of the desktop program screen and then click on New Tax Return.