I downloaded the XCode Beta 8 and converted all of my swift code from Swift 2.3 to Swift 3. It has caused way too many problems for me and caused me to start a project I\'ve
I feel you. Also learned this lesson the hard way!!
What (kinda) worked for me was opening the project in XCode 7.3.1 which reduced the errors from 230+ to 60. I was able to revert to Swift 2.2 manually doing changes such as changing Data back to NSData. If you know what changes Swift 3 made (Google it) then you might be able to fix most of your project.
Good luck!