Why my iPhone region is stuck in China ?

Hey Gos5,

You can find the steps to change your Apple ID region here: Change your Apple ID country or region

"Use your iPhone or iPad to change your region

1. Open the Settings app. 
2. Tap your name, then tap Media & Purchases.
3. Tap View Account. You might be asked to sign in.
4. Tap Country/Region.
5. 
6. 
   
7. Tap Change Country or Region.
8. Tap your new country or region, then review the Terms & Conditions.
9. Tap Agree in the upper-right corner, then tap Agree again to confirm.
10. Select a payment method and enter your new payment information and billing address, then tap Next. You must enter a valid payment method for your new country or region.*

"

If you're referring to the region of your iPhone's hardware, that would not be something that can be adjusted as it would be based on the region the device was manufactured for.

Thanks!