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...
