Resetting the network settings on your iPhone can resolve network connection problems. Note: Performing this action will delete all network settings, including saved Wi-Fi networks and Bluetooth connections. It will not delete any apps, data, or contacts.
From your home screen, tap Settings.
Scroll down and tap General.
Tap Reset.
Tap Reset Network Settings.
The iPhone will automatically reset and reboot. Once your device boots back up, all your settings have been reset.