https://wccftech.com/download-ios-12-beta-4/

You can now download iOS 12 Beta 4 for your iPhone, iPad or iPod if you are a registered developer with Apple.

Right on cue, Apple has released for download iOS 12 Beta 4 to registered developers. It’s available for all compatible devices that can run iOS 11, namely all of the 64-bit devices from Apple’s mobile lineup. This means that even if you have an iPhone 5s, the latest beta will be available to you, provided you are a registered developer with Apple, of course.