Reset iPhone without wifi or cellular data

You could try using a computer to help you with resetting the phone:

The guide can be found here: Erase iPhone - Apple Support (MY)

You can use a Mac or Windows PC to erase all data and settings from your iPhone, restore iPhone to factory settings, and install the latest version of iOS.

1. Connect your iPhone to your computer with a USB or USB-C cable. You may also need an adapter. See Connect iPhone and your computer with a cable.
2. Turn on your iPhone.
3. Do one of the following:

• • On a Mac (macOS 10.15 or later): Click the Finder icon in the Dock to open a Finder window, click the iPhone button in the Finder sidebar (below Locations), click General at the top of the window, then click Restore iPhone.
  • On a Mac (macOS 10.14 or earlier) or a Windows PC: Make sure you have the latest version of iTunes (see the Apple Support article Update to the latest version of iTunes). Open iTunes, click the iPhone button near the top left of the iTunes window, click Summary, then click Restore iPhone.

Take the phone down to the coffee place and log onto the Wi-Fi there. Will only take a few minutes.

Maybe you can borrow your friend's hotspot for awhile. The iCloud checking is short and for the rest of the reset process you won't need an active connection to the internet.