IOS 12 is now available for public. they can download this update by simply signing on apple website
iOS 12 public beta: Compatible devices
iphone - 5s , SE , 6 , 6s , 7, 7+,8,8+, 10
ipad - 12.9-inch iPad Pro 2nd generation, 12.9-inch iPad Pro 1st generation, 10.5-inch iPad Pro, 9.7-inch iPad Pro, iPad 6th generation, iPad Air 2, iPad Air, iPad Mini 4, iPad Mini 3, iPad Mini 2
ipod-iPod Touch 6th generation
TAKE ICLOUD BACKUP BEFORE UPGRADING TO IOS 12 !
HOW TO ENROLL FOR PUBLIC BETA?
Go to beta.apple.com on your iPhone, iPad, or iPod Touch.
Tap Get started.
Now you will be asked to enroll your device which will require signing in with your Apple ID.
Tap Agree to the Terms and Conditions.
Tap Agree to confirm again.
THANKS ENJOY YOUR EXPERIENCE