Was the 2016 return prepared in Online TurboTax (website version?) If prepared in desktop software (CD/download), the *.tax2016 data file and any PDFs would be stored locally on your computer or external media.
If the 2016 return was prepared online, log in and go to the Tax Home page. It may already open by default on the Tax Home page. If not, you can click Tax Home in the left menu column. Then on the Tax Home page scroll down to "Your Tax Returns & Documents". Click on that line or on the word "Show" to expand that topic Then you should see a list of prior tax years. Click on the one you need.
If you do that, but find no evidence of the 2016 return, then you likely have multiple accounts and signed into the wrong one. To get a list of your User IDs and recover account access, you can use the tool at the link below. Try using your phone number first. After that, if necessary, then run the tool on your email address(es) you can access.