Did you prepare and NETFILE the original return using TurboTax Online? If you did, you need to go back to the original return to REFILE it. Please see this TurboTax FAQ for instructions on how to use REFILE: I've filed my tax return. Can I still make changes?

If you didn’t prepare the original return in TurboTax Online, then you won’t be able to use REFILE. The software will try to send the return you prepared via NETFILE, which will not work.