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To revert to your carrier's default APN information, go to Settings > Cellular > Cellular Data Network > Reset Settings. If you installed a configuration profile, the profile's default information will be used instead.
If you're using an iPhone or iPad in an enterprise environment, your IT manager might have set up a special APN for you to use. If this is the case, contact your IT manager to change your APN. If you change an APN that an IT manager set for you by using a configuration profile, you can tap Reset Settings to change it back:
- iPhone: Tap the Reset Settings button in Settings > Cellular > Cellular Data Network.
- iPad: Remove the configuration profile and add it again.
For more information, contact your IT manager.
If you're an IT manager, you can use Apple Configurator, OS X Server Profile Manager, or another Mobile Device Management solution to change advanced settings on an iPhone or iPad, including the APN.
Learn more on iOS Enterprise Deployment Resources and the iPhone Enterprise Support site.
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copied from: View and edit your Access Point Name (APN) on your iPhone and iPad - Apple Support