How can I fix the network error with IOS update 12.0.1

or maybe the network needs to do a update. if you go to settings>general>about normally if there is a carrier update it will do it automatically. or connect your iPhone to iTunes and then also if there's a carrier update it should pop up saying carrier needs to do an update

have you tried turning the iPhone off and then back on

or have you tried taking the sim card out wipe it and then put it back in. try that