Cellular data update

This is not an iOS update.

Go through the various suggestions in the support article below

https://support.apple.com/en-us/HT201415

Should fix it but they don't help, and your network carrier can't help, then  contact Apple Support for further investigation.

 contact Apple Support

Support article:

Hi,

Try to update your carrier settings in Settings > General > About

If still unable to update the carrier settings, reset your network settings in Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings

https://support.apple.com/en-us/HT201415

Hope this helps!

It says it needs a carrier update. If repeatedly "hot" SIM removal and re-insertion does not stimulate a carrier update then talk to your carrier, especially if the phone is locked to them.

(If not carrier locked then borrow a different carrier SIM from a friend.)

If they can't help then reach out to Apple Support directly. Depending on your region, you may be able to reach them here: contact Apple Support 

or visit an Apple store.

If anyone else is reading this, if your phone says it needs an update to get service, NEVER reset the phone as you will have a heck of a job to re-activate it without service.

Simply go to Settings, General, About and accept the carrier update.

That photo is unreadable.

If it says No Service then with the phone turned on, take out the SIM and put it back.

Or try another compatible SIM

ps it isn't unreadable, because it knows that YOUR carrier needs an update to get service.