Turn Your iPhone Off and Back On
It may sound like a cliché, but turning your iPhone off and back on does help fix many issues. Chances are good that it will fix your cellular problems, too. There’s certainly no harm in trying.
How you turn your iPhone off will depend on which model you have.
If your iPhone has Face ID, you’ll need to press and hold the side button and one of the volume buttons at the same time until the Power Off slider appears.
If your iPhone has a Home Button, then press and hold the side button until the Power Off slider appears.
Swipe the slider to the right and keep your iPhone turned off for about 30 seconds. Then, press and hold the side button until the Apple logo appears on your screen.
Once it’s turned on, check if the cellular is working again.