If you actually want to "go back to 2016", you need a time machine, which can be difficult to obtain. However, if you want to remain in 2019 and just use the 2016 software (you may need to re-license the software under the "Tools" menu), that is fairly easy. 
From a different perspective, if you've got Doc and the DeLorean, you don't need to relicense the software by just going back to 2016 or 2017 and the return will be timely. 
