My phone did not complete an update and I do not have cellular data now how do I fix that

If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

Update your carrier settings on your iPhone or iPad - Apple Support...you may need this...

Try this first...Reset your Network Settings.

Go to Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.