You'll want to wait until your returns have been accepted before you mail in your amendment. And yes, you'll need to mail it in, unfortunately.
But to do the actual amending process, just:
- log in to TurboTax,
- scroll down until you see Your Tax Returns and Documents,
- click Show,
- and the top option in the right-hand sidebar is Amend (change) return.
Just click through there and you'll be on your way.
