: Modifying firmware typically voids your manufacturer's warranty. OPPO Global Community Conversion Requirements
: Download the specific "Convert to Global" firmware files (often labeled for the CPH1701 model). oppo a57 china to global firmware
After converting, accept an OTA (Over-the-Air) update from OPPO Global. It will likely reset your modem and may lock the bootloader again. Turn off automatic system updates in Developer Options. oppo a57 china to global firmware