Were the 2016 returns prepared with Online TurboTax? If so, log in and at the Tax Home go to the section "Your Tax Returns & Documents." Click to expand. Choose tax year 2016. Then choose "Download/print the PDF."
If you find no evidence of an online 2016 return in that account, then we can tell you how to look for multiple accounts.
If you do find evidence of the 2016 returns, but when you click to download/print, it asks you to pay, report back. If access is locked, then the method to pay to unlock it depends on what all you have done for your 2018 return.
If that's what you encounter, please answer these:
Have you already filed a 2018 online return, or is it still in preparation? Or did you file one elsewhere?
Is your 2018 return in Free Edition or a paid edition?
Is the 2016 return in the same account as your 2018 return?
