Many people have multiple TT accounts and forget how to access them. Log out of the account you are in now.
Account recovery
https://myturbotax.intuit.com/account-recovery/
https://ttlc.intuit.com/questions/1901535-forgot-your-turbotax-online-user-id-or-password
Or did you use the desktop version of TurboTax? If so, the files are on your own hard drive or any backup device you used like a flash drive.
https://ttlc.intuit.com/questions/1901486-how-many-turbotax-accounts-do-i-have
https://ttlc.intuit.com/questions/1901535
. If you have any changes/corrections at all to make to your 2018 return, you now have to complete it using desktop software, which you must download to a full PC or Mac (not to a mobile device).
If you already paid for your online software you can ask customer support for a download of the desktop software.
They are available from 5 a.m. to 5 p.m. Pacific time Monday-Friday.
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number
If you are getting a refund, there is no penalty for filing late. If you owe tax due, then file and pay the amount due as shown on the Form 1040, but expect a bill later from the IRS for the penalty and interest you will owe. Only the IRS will calculate this—TurboTax will not calculate it.
It just occurred to me---- if you are trying to use the 2018 AGI on that unfiled 2018 return so that you can e-file 2019, it will not work since it never made it into the system.
For your 2018 AGI try using zero, but if zero does not work, you will have to print, sign and mail 2019.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.