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
<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/3449967-amend-prior-year-return-mac-software-request">https://ttlc...>
If you go to the link that VolvoGirl posted above, and click through the appropriate links for the year and how you filed the original return, it will lead you to this same request form.
You can amend your 2016 tax return online until October 15. Earlier years cannot be amended online. If you do not have the CD or download TurboTax software for the year that you have to amend, you have to install the amendment software on a Windows or Mac computer. Again, if you follow the links that VolvoGirl gave you, they will lead you to step-by-step instructions for your particular situation.
You must have a copy of the original tax return you want to update.
The simplest way is to prepare your correct tax return (using other software not involving Windows) and print it.
Then lay the paper printouts of both returns (correct and original) side-by-side.
You now have all the information needed to prepare Form1040X by hand. It's pretty straight-forward.
The blank form in writeable PDF format and its instructions are available at www.irs.gov.
Mail to the same address you would mail your original tax return.