How to resolve an iPhone hardware issue affecting cellular network connection?

I need to clearly answer, what if Diagnostic detected an issue of iPhone hardware, and it doesn’t support cellular network connection . How i can do i have used only 1 years i dont have any problem with my phone only this problem. May i know iphone centre will be repaired to my phone without cost and if they cant do repair without money, what will cost for repair price. I would be possible like change phone or other

[Re-Titled by Moderator]