Hi my phone has a cellular issue detected what will i do

 As a start I would...

Manually update your carrier settings on your iPhone or iPad - Apple Support

The article you came to the community from If you see a Cellular, Ultra Wideband, or Apple Pay Issue message after an iOS update or restart is the best resource for this situation. If you've completed that troubleshooting and the issue is still not resolved, use the link in the article to Contact Support.

Click here > Contact - Official Apple Support

or phone numbers 

Click here > Contact Apple for support and service - Apple Support