Get your taxes done using TurboTax

What year do you need to amend?  You can only amend the current 2016 return online.
How to amend 2016 online, https://ttlc.intuit.com/questions/3402261-how-do-i-amend-my-2016-turbotax-online-return

For prior years you need to use a Windows or Mac computer
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed