For iPhones it should automatically be recognized for public mobile. If not try to switch networks to another one and then back to public mobile.
If that does not work try rebooting the phone. If that does not help then try a network reset. It will get rid of all previously saved networks back to factory settings. That normally does the trick
@Ken4 reset your network settings.
Restart your phone if it doesn't, reenter your wifi if applicable, enable data and sms and mms to send and receive from Android phones. Try surfing the internet. Stay safe.