It'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
If you used the Desktop CD/Download program then the only copy is on your computer and not saved or stored online.
Or is the IRS saying you didn't pay a tax due?
If you don't find your 2018 tax return in a different account, see the following FAQ for some other possibilities.
Did you use TurboTax to file your 2018 tax return? If you used other software, or someone prepared the return for you, it won't be in TurboTax.
Of course, if you can't find your 2018 tax return anywhere, there is one last possibility. Maybe the IRS is right. Maybe you never filed for 2018.
And....does the IRS say you did not file for 2018---or that you did not pay your tax due for 2018? If they are saying you did not pay the tax you owed, then your only proof that you paid will be your own bank or credit card statements showing the payment.