If I filed my 2018 taxes why can't I find the tax return on file with turbotax ?
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.