Qualcomm USB Drivers: Install the latest Qualcomm HS-USB QDLoader 9008 drivers on your Windows PC so the computer can recognize the phone in EDL mode.
Oppo A57 (CPH1701) Official Flash File Guide: Download and Installation oppo a57 cph1701ex-11-a.35 flash file
Follow the on-screen prompts and restart your PC once installation completes. Step 3: Boot Oppo A57 into EDL Mode Qualcomm USB Drivers: Install the latest Qualcomm HS-USB
Install OPPO USB Drivers on your computer to ensure the phone is recognized. oppo a57 cph1701ex-11-a.35 flash file
Reinstall the Qualcomm USB drivers or try a different USB port (preferably a USB 2.0 port on the back of the PC).
Click the (or Start All ) button in the top right corner of the tool window.