To add to what Hallux said you need to flash a ROM with the old software into the phone using Odin. I wouldn't recommend doing that with such a new phone, especially if you aren't very tech savvy. It involves a fresh install of the Android removing all of your data, voids your warranty, prevents you from getting security updates, and will brick your phone if you screw up.
I know software changes can be annoying, but it's an annual thing, eventually you will need to adapt to the changes.