After you file

You only need to sign onto to  TurboTax using the exact same User ID you used for the Free File program - https://myturbotax.intuit.com/

You will get the info about FREE FILE no longer being supported then choose to start with the online program even if you will not use it.  Once you get thru the personal information you will land on the home screen where you can scroll down and pick the tax year you want then choose to amend ... follow the screen instructions.