My phone is saying that my “ celular update failed “ and I don’t know how to fix it

If reset network settings doesn’t fix it (it probably won’t) you need to restore your phone using your computer—>If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

If it says there is no update chose Restore instead.

Try to reset network settings

this can be found in settings, under general, then reset.

it will clear all of your cellular and WiFi settings.