How do I update if I don’t hav WiFi?

Use a computer. Or use some other Wi-Fi, such as at an Apple Store.

Details: Update your iPhone, iPad, or iPod touch - Apple Support

Cellular updates and cellular backups are becoming possible with 5G cellular devices, too.

Nonono70 Said:

"How do I update if I don’t have wifi"

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Use of Ethernet:

If you use a computer, try connecting the computer to Ethernet, if WiFi is of no option on the computer, even. You would connect the computer through Ethernet, going directly into your router. For a Mac (or PC) that does not have Ethernet, this would be the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple

Hi there,

You need an Internet connection to update iOS. You can also update your iPhone using a computer.