The third beta of iOS 13 has just been released, coming with several subtle changes, mainly on Apple Arcade and FaceTime. Registered developers will need to download the profile for the iOS 13 and iPadOS betas from Apple's Developer Center, while the users of 3uTools are able to do it on 3uTools directly.
Here is how you can update the iOS 13 beta 3. Please note that iOS 13 beta 3 doesn't initially support iPhone 7 and iPhone 7 Plus.
Step 1 Connect your iDevice to PC with an original USB cable and launch 3uTools.
Step 2 Go to Flash & JB → Easy Flash, select firmware iOS 13.0beta3. If you want to update with data, please check the box "Retain User's Data While Flashing". There will be a pop reminder after you click "Flash", please read it with caution.