If you are looking for software to file your 2016 return, you can purchase and download here: https://turbotax.intuit.com/personal-taxes/past-years-products/
Here's an article that outlines how to approach filing returns for prior years: https://turbotax.intuit.com/tax-tips/irs-tax-return/how-do-i-file-back-tax-returns/L535BxMms