You need to log in to the account you used for that year. If you need to amend 2017 or prior you need to download the .tax file and use the Desktop amend program. You can amend 2018 online.
That's common to end up with multiple accounts. First LOG OUT of whatever TurboTax account you're logged into right now. Then use this TurboTax account recovery website to get a list of 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 you used the Desktop CD/Download program then the only copy is on your computer and not saved or stored online.
