1. Open the settings option on iPhone6, and click iTunes Store and App Store to enter.
2. Log in to the Apple ID account in iTunes Store and App Store, click View Apple ID Account, and enter the Apple ID password.
3. Open the country/region option in the personal Apple ID account information and select Change Country/Region.
4. Change China into the United States or other countries, and complete the information after modifying the country.
5. After completion, opening iBooks on iPhone6 will not make the display unavailable.