Sorry online is only for 2017 now. So you have to buy the Desktop CD/Download program here https://turbotax.intuit.com/personal-taxes/past-years-products/
Or you can get the blank forms from the IRS and do them by hand. Either way you will have to print and mail prior year returns. And send each year in a separate envelope so the IRS doesn't miss any.
You should clear your 2016 info out and use it for 2017. How to clear and start over https://ttlc.intuit.com/questions/2586254-using-clear-start-over-in-turbotax-online
