See this TurboTax support FAQ for completing a 2018 tax return originally started using the online editions - https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...
You have to sign onto your 2018 online account using the exact same user ID you used to create the 2018 online 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"
If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created. TurboTax does not store online any returns completed using the desktop editions.
If you still cannot access your account, you can contact TurboTax customer service/support through their contact website during business hours.
See this TurboTax support FAQ for a contact link and hours of operation - https://ttlc.intuit.com/questions/3401489
Submit your question/problem during business hours and then use the option for Call (a phone number will be provided for Call) to speak directly with a TurboTax agent -
Note: The Call option will not be available when TurboTax Support is closed.