How can I update using mobile data?

You don't sorry.

Your iPhone MUST be connected to reliable and fast wifi network with Internet access. That condition is mandatory to update an iPhone (no cellular data, no personal hotspot, no VPN connections are allowed). And your iPhone's battery should be over 50% level (better if plugged into power).

That said, if you don't have a wifi network, "borrow" one from your friends/neighbors, or ask for help at an Apple Store or Authorized Service provider.

Regards

Giulio

They might be using 5G on iphone 12 series, or their device is not an iPhone.

Unless you're talking about updating "apps". They can be updated using cellular data (if their size is under 200MB).

Regards

Giulio

You can't.

Unless you have one of the iPhone 12 models with 5G.