You have to sign onto your 2018 online account using the exact same user ID you used to create the account.

Close all TurboTax windows on your web browser (including this one).  Copy and paste the account recovery website link onto a new web browser window and run the tool.

Use this TurboTax account recovery website to get a list of all the user ID's for an email address.  Run the tool against any email addresses you may have used - https://myturbotax.intuit.com/account-recovery

If none of the user ID's received will access your 2018 account, then use the option shown in blue on the account recovery website, "Try something else"

To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/

Scroll down and on the section Your tax returns & documents click on Show.  Click on the Year and Click on Download/print return (PDF)

Or -

When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state.  See screenshot

This will take you back to the 2018 online tax return.

Click on Tax Tools on the left side of the online program screen.  Then click on Print Center.  Then click on Print, save or preview this year's return.  Choose the option Include government and TurboTax worksheets