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.

Hi there,

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

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