How can I update my iPhone without WiFi

If you have a Mac or PC handy, you can update your iPhone using iTunes. While in iTunes, plug your phone into the PC or Mac. It should show up in the iTunes Summary tab. Click Check for Update, and update from there. I advise you use iTunes to back up your iPhone data before updating.

Good luck!

https://support.apple.com/en-us/HT212186

You can't.

You must have a stable Wi-Fi connection.

Only iPhone 12 models with a strong 5G connection can update using mobile data.