How to Downgrade from iOS 10.3 Beta to iOS 10.2.1
Here's how you can downgrade from iOS 10.3 beta to iOS 10.2.1 on your iPhone, iPad or iPod touch device.
Roll Back to iOS 10.2.1 if iOS 10.3 Beta is Not Cutting it for You
iOS 10.3 beta is finally here, but it might not just be for everyone due to its 'pre-release' nature. If you think you have made a mistake upgrading to the aforementioned firmware, then you will be pleased to learn that you can downgrade back to iOS 10.2.1 in a few easy steps. But keep one thing in mind though, this will erase everything off your device. Even if you take a backup of your stuff on iOS 10.3 beta, there's no way you can restore it onto iOS 10.2.1 as backups aren't backwards compatible. With that out of the way, let's jump into the downgrade process itself.
Tutorial - Downgrade iOS 10.3 beta to iOS 10.2.1
Before going ahead with the downgrade process, make sure Find My iPhone is disabled on your device. You can turn it off by going to Settings > iCloud > Find My iPhone.
1. Download the iOS 10.2.1 final firmware file and place it on your desktop for safekeeping: Download: iOS 10.2.1 IPSW for iPhone, iPad, iPod touch Released.
2. Download and install iTunes on your computer if you haven't already. You can do so by going to: apple.com/itunes
3. Assuming you are done with steps 1 and 2, now connect your iOS 10.3 beta device to your computer using a Lightning cable.
4. iTunes should automatically launch once you connect your device. If it does not, then do so manually.
5. Let iTunes refresh properly. Once done, click on your device at the top left hand corner of iTunes.
6. Now click on the Restore iPhone button while holding down the left SHIFT key (Windows) or the left OPTION key (Mac). A new pop-up window should come into view.
7. Select the iOS 10.2.1 firmware file you downloaded in step 1 and let iTunes work its magic.
The downgrade process will now begin. iTunes will first extract the firmware, prepare your device, restore the firmware and then verify the restore process with Apple. If everything goes smoothly, you will see a welcome screen on your iOS device. Just set it up as you normally would and start using it.
iOS 10.3 is currently sitting on its first ever beta release. This means there are going to be bugs around corners where you least expect them to be. It's recommended to install the firmware after at least three beta builds are available to developers. If you are wiling to take the plunge before that, it's totally your call.