Cannot edit the "Release Date" field for TV shows in iTunes
You can "import" a TV show episode from the Windows system to your Mac, set the release date on the Mac and then copy it back to the Windows system. Not exactly a viable workaround for most but if you happen to have both platforms it may work until Apple gets their act together and starts to test their software before releasing it to their customers.

Quoted from Apple's Support Forums: https://discussions.apple.com/thread/7567758?start=0&amp;tstart=0

Seems like this is an issue for many and you might have to wait for a newer version.