Apple released the first minor update to iOS 12 today, fixing two bugs. The new version is available as part of the software updates on iPhones and iPads with iOS 12. You can wait for the notification, or go to Settings, General, Software Update.
The bug fixes include an issue where some iPhones weren’t charging when connected with a cable. It also fixes an issue with where a slower Wi-Fi connection was selected when a faster one was available. The keyboard on the iPad will also now see consistent placement of the number key in the lower left corner. Bluetooth and video subtitle bugs are also addressed.