I'll first tell you how to look for your old account from 2018. Then in a separate comment, I'll give you some more info on ways to get the 2018 AGI.
Many people end up with multiple accounts without realizing it. Here's how to troubleshoot for multiple accounts (User IDs) :
You can have up to 5 accounts that use the same email address for notification purposes. A User ID may be an email address, but it doesn't have to be. It might be only part of an email address, or it can be anything at all.
To get a list of your User IDs and recover account access, you can use the tool at the link below. Try using your phone number first. After that, if necessary, then run the tool on your email address(es) you can access.
NOTE: Before running the account recovery tool below, log out of all Intuit accounts including this user forum, or you might end up in a loop. Then clear your browser Internet cache, close your browser, then reopen it, and go to the link below. You may wish to copy this link so you can paste it into the new browser session.
If still no luck after running that on your phone number and email address(es) that you can access, here's another method:
Go back to the tool again, but this time leave the data field blank, and choose the small blue link that says "Try something else", and it will look you up by SSN and other parameters.
Hopefully, you are able to find your 2018 return with the above info.
Another option is to download a 2018 return transcript at the IRS, if you are able to open an IRS account there.
Here's a FAQ on getting the 2018 AGI:
If you still need help, then as I mentioned in your other thread, Free Edition does not have phone support unless you upgrade to PLUS for 29.99.
You could contact a support agent directly with messaging at Twitter or Facebook and see what they advise:
NOTE: When efiling the 2019 return, be sure you enter the 2018 AGI from the original 2018 return--not from any 2018 amended return (if applicable). If your return keeps rejecting for the incorrect AGI reason, you can print, sign, and mail it to the IRS.