Not all iOS Beta updates are "pink", and not everyone is happy, especially with the newly released iOS 13 Beta. I instructed to restore old iOS devices (12.3 and 12.3.1, 12.3.2) for those who want to downgrade, although basic but hope to be useful for you.
Turn off "Find my iPhone / iPad / iPod" (should do)
Anyway, the iOS device will ask you to turn it off during the restore process, so it's best to turn it off first.
To enter Settings (Settings) – Apple ID – Find My – Find my iPhone / iPad / iPod – turn it off
Download the old iOS version to your computer to restore
I share the entire IPSW file for you, including iOS 12.3 and iOS 12.3.1, iOS 12.3.2 exclusively for iPhone 8 Plus. Which one do you use, click on download the appropriate IPSW:
Proceed to install
After plugging the connection between your iOS device and the computer, go to iTunes / Music, if it's a Mac computer, hold down the Option key and select Restore (as shown above). If it's a Windows computer, hold down Shift.
Then select the IPSW file you downloaded earlier
Click "Restore" to confirm
If, before going to iOS 13, you have backed up the old version, you reset all the devices so that it returns to the original active state. To enter Settings (Settings) – General settings (General) – Reset (Reset) – Delete all content and settings (Erase all Settings & contents).
Turn on the device and login to Apple ID again, you can choose to Restore from iTunes Backup, of course, now you have to plug in the iOS device connected to iTunes on the computer. Then select Restore the backup you have done before that is done.