These guides provide visual walkthroughs for flashing stock firmware and performing a hard reset on the Oppo A9 2020:
Released in late 2019, the Oppo A9 2020 (model number CPH1943) was a standout mid-range device, offering a large battery, a quad-camera setup, and the Snapdragon 665 processor. While the device has aged gracefully in terms of hardware, software updates are crucial to keeping it running smoothly. Oppo A9 2020 Firmware