HOW TO CHANGE REGION ON IPHONE

Open the Settings app.

Tap your name, then tap Media & Purchases.

Tap View Account. You might be asked to sign in.

Tap Country/Region.

Tap Change Country or Region.

Tap your new country or region, then review the Terms & Conditions.

Tap Agree in the upper-right corner, then tap Agree again to confirm.

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.*

Also you can change your region Online 

Change your region online

1. 1. Sign in to account.apple.com.

2. 2. Tap or click Personal Information.

3. 3. Tap or click Country/Region.

4. 4. Follow the onscreen instructions. You must enter a valid payment method for your new country or region.*