How do I amend my 2019 federal tax return online using TurboTax?

Sorry you can no longer use Turbo Tax to prepare or amend a 2019 return.   Not Online and not using the Desktop program.  You need to do it yourself or go to a local tax place or accountant.

@krystyle82 why are you attempting to amend 2019?  The deadline to claim a refund for a 2019 tax return was July 15, 2023.....  if you owe, you owe.