How to install or uninstall iOS beta software:
This is an article straight from Apple that will help you with downgrading from an iOS Beta:
Uninstall iOS beta
To uninstall iOS beta, you need to erase and restore your device. Then if you have an archived backup you can set up again from that backup. Here's how:
1. Check that you have the latest version of iTunes.
2. Connect your device to your computer, then put your device in recovery mode with these instructions:
- For iPhone 6s and earlier, iPad, or iPod touch: Press and hold the Sleep/Wake and Home buttons at the same time. Don't release the buttons when you see the Apple logo. Continue to hold both buttons until you see the recovery mode screen.
- For iPhone 7 or iPhone 7 Plus: Press and hold the Sleep/Wake and Volume Down buttons at the same time. Don't release the buttons when you see the Apple logo. Continue to hold both buttons until you see the recovery mode screen.
3. Click the Restore option when it appears, which erases your device and installs the current non-beta version of iOS.
4. Wait for the restore to finish. If asked, enter your Apple ID and password, which disables Activation Lock. If the restore process won't finish, get help.
After the restore finishes, you can set up your device from your archived backup, which should be from an earlier version of iOS.
If you back up a device that has iOS beta, the backup wont work with earlier versions of iOS. For example, if you go back to iOS 10.3.3 from iOS 11 beta, a backup you made while using iOS beta wont restore. Instead, restore from a backup that you made before you installed iOS beta.
Hope this helps.