If you used the Online version it is only good for 1 return per account so the last one done overwrites the prior ones and they are gone for good. Do you have more than 1 account?
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 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.