My iPhone 7 have error

hello. I’m Cong.

I live in Vietnam. I'm using iPhone 7, and it's out of warranty for Apple. I use it normally, until I upgrade to IOS 12.1.4 then it has an error. My iPhone 7 is not active inside. along with the "no service" notice "looking for". And I found my device imei information gone. Can you show me how to fix?