Two days after releasing the final version of iOS 12.2 for all users, Apple is today starting a new beta cycle with the release of iOS 12.3 beta 1. The update is available in 3uTools now, here is how to upgrade without losing data.
Step 1 Connect your iDevice to PC with USB cable and launch 3uTools.
Step 2 Navigate to Flash & JB → Easy Flash, and select iOS 12.3 beta. After you click Flash, there will be a popup reminder and please read it with caution. If you want to save your data, please check the box "Retain User's Data While Flashing".
Please back up your iDevice regularly just in case.
Step 3 Keep a good connection and internet while flashing, wait patiently for around 5 to 10 minutes. Your device will be restored to iOS 12.3 Beta after reboot.