TurboTax online and e-file for 2018 ended on Oct 15, 2019. 2018 (and earlier tax years) can now only be completed using the CD/download software installed on a Mac or Windows computer. The return must be printed, signed and mailed.
2016-2018 software can be purchased here:
Did you file it? You now have a problem. You have to file each year separately. Online is only for 2019. You have to wait and see if your efile gets accepted. If they reject it for something you can change it around to be only for 2019
But if they accept it you need to wait some more for it to fully process and you get the first refund. Then you need to Mail in an Amended 1040X return to change it to be for 2019.
You can check your efile status here https://turbotax.intuit.com/tax-tools/efile-status-lookup/
How to amend an Online return
Amended returns can only be MAILED not efiled.
Then if you still need to do 2018. To do 2018 you have to buy the Desktop Download program here
Or If you have a simple return You can fill out the blank forms for free.
Here is the IRS 2018 Form 1040
And instructions https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-prior/i1040tt--2018.pdf
IRS 2018 Schedules 1 thru 6 (only if needed)
Don’t forget your state. And you will have to print and mail your returns. So be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.