If you have not filed your tax return yet, just log in to your account and start deleting everything that should not be on your 2019 tax return. If you haven't yet filed for 2019, you can then enter your 2019 information before you file your return.
If you have already efiled your return and it has been accepted or if you have printed and mailed your return, you will now have to prepare, print and mail an amended return 1040X for 2019 to fix the problem. DO NOT change anything on your return until you start the amended return.
If you have not yet filed your correct 2018 tax return, you must buy, download and install on your computer the 2018 program: https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2018 return must be printed and mailed. It can no longer be efiled. You must print and mail it yourself because TurboTax doesn't print and mail it for you. Use the filing instructions that print with your return for what to include and where to mail it.
The IRS is currently not processing any mailed returns. They have not said when they will start up again.