Hello i have question why my iphone no detect my sim ?

See if anything here helps.

 iPhone - How to unlock for use with a different carrier.  

iPhone – Won’t activate.        

iPhone/iPad - No Service or Searching.  

iPhone - If you can't make or receive calls

Sounds like you got a carrier locked iPhone.

To use a different SIM card, the carrier that locked the iPhone must officially unlock, not Apple or anyone.

You have to ask them and if you qualify.

I found out that certain models of the iPhone 7 have “known” network issues that Apple has to fix. Not sure if this would apply to you. The is with T-Mobile/Sprint currently.