You cannot add it to your 2016 return. You can amend your 2015 return.
https://ttlc.intuit.com/questions/2952222-how-do-i-amend-the-2015-taxes-i-filed-with-turbotax-online
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
