The iPhone will normally retrieve the default settings for connecting to a mobile data network from the SIM card or receive them automatically via the network. You can also set up the mobile data connection manually on your iPhone. Here's how:
Tap Settings.
Scroll down and tap Mobile Data.
Enable Mobile Data.
Tap Mobile Data Network.
Edit the details for Mobile Data as follows:
Tap Mobile Data.
To finish the process and activate the settings, you need to restart the device. Your iPhone will then be configured to use mobile internet.