https://wccftech.com/apple-releases-second-beta-of-ios-13-4-macos-catalina-10-15-4-watchos-6-2-tvos-13-4-to-developers/

Apple has seen fit to release the second beta of iOS 13.4, macOS Catalina 10.15.4, watchOS 6.2, and tvOS 13.4 to developers for testing purposes. The latest beta build arrives two weeks after the company seeded the first developer beta. If you're a developer and want to test the latest beta firmware for yourself, you can download it right now on your compatible devices from the Apple Developer Center.

iOS 13.4 and iPadOS 13.4 beta 2 can be downloaded on your iPhone and iPad from the Apple Developer Center. Do take note that a proper configuration profile is required which can be installed from the Apple Developer Center. On the latest iPhone models with A13 processors, Apple requires you to install the beta through over the air mechanism using the configuration profile.