My wifi not working

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support

If Wi-Fi isn’t available to you, visit an Apple Store and you may use their Wi-Fi.

redoy97 Said:

"My wifi not working: My wifi not warning so I can’t download iOS 15 update in mobile data"

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Have 5G Available?:

As long as your iPhone is iPhone 12 with 5G capabilities, and as long as 5G is an option in your current area, then the updating is expected to go though. Go here: Use an iPhone 12, that is using 5G in order to update over Cellular - User Tip