This answer assumes your 2018 return was prepared in Online TurboTax. Any return prepared in desktop software will not be in an online account.
Also see the 2 methods and video here first:
FAQ: How do I access my prior year return?
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/01/270...
Log in and click on the Documents tab in the left menu column, and then a dropdown list of years should appear. Choose the year 2018, and then way off to the right of the screen, you should see a link to download the PDF. If that didn't work, here's another method:
Go to the Tax Home. Scroll down the Tax Home page to the section "Your Tax Returns & Documents." Expand that section and choose the tax year you want. Then you can choose to "Download/print the PDF".
If you do all that, but there's no evidence of prior returns in the section "Your Tax Returns & Documents", then you likely have multiple accounts and signed into the wrong one. Many people end up with multiple accounts.
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, reset password, and recover account access, etc., you can use the tool at the link below. When using the Account Recovery tool, try using your phone number first if you can still access it. 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.
https://myturbotax.intuit.com/account-recovery
If still no luck after running that on your phone number you can still access 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, scroll down a bit, then choose the small blue link that says "Try something else", and it will look you up by SSN and other parameters.
One of the methods above should find a copy of your actual 2018 return PDF if it was prepared in Online TurboTax and if you are in the correct account.
It's also possible to download a free 2018 tax return transcript at the IRS website below if you qualify to open an IRS account. Otherwise you can order one through the IRS website to come by postal mail in 5-10 days.
https://www.irs.gov/individuals/get-transcript
A copy of the actual return from the IRS costs $43 and takes several weeks.
