Users with the China-specific version (A57t or regional models) often flash the global ROM to gain access to Google services.
For most users, the safest way to update is Over-The-Air (OTA). oppo a57 global firmware
Just like a factory reset, but deeper. Flashing firmware rewrites every system partition, clearing out corrupted cache, orphaned files, and malware. Users with the China-specific version (A57t or regional
"To flash: Copy the .ozip file to your phone storage. Go to Settings → About Device → Updates → Local Install. Select the file." clearing out corrupted cache