You'll need the 2016 software in order to amend that return. So if you paid and filed using TurboTax last year, go here How do I amend my 2016 TurboTax Online return? and follow those steps to get the amend software.
Once you have the software downloaded, follow steps here How do I amend my 2016 return in the TurboTax CD/Download software? to help you amend that return.