As of October 22, TurboTax 2016 online is shut down and can no longer be used to amend 2016. You must use the amend desktop software on your computer to amend.
2016 amend software:
https://turbotax.intuit.com/personal-taxes/cd-download/amend/ty16/
Get a copy of 2016 tax file to amend:
https://ttlc.intuit.com/questions/1899645-how-do-i-save-my-2016-turbotax-online-return-as-a-tax-data...
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
