Apple has released the fifth iOS 10.3.3 beta for iPhone, iPad, and iPod touch for public testers. Users could flash this verison in 3uTools. The beta version only includes new wallpapers for the 12.9-inch iPad Pro and no other visible changes, although the release may be the last bug fix update for devices not able to run iOS 11.
Step1: Make sure that you have the latest version of 3uTools. Before upgrading, you should backup your iDevice. Connect your device to your computer, click the button ”Flash & Jailbreak", click the button “Easy flash”.
If you want to retain the data, please select the option " Retain User's Data While Flashing".
Step2: Select the firmware iOS 10.3.3beta5 , and then click the button “Flash”. (If you have downloaded the firmware, you need to import it to your PC first, and then flash your iPhone).
Step3: Keep a good connection between iDevice and PC, and then just wait until this process is finished.