You need QPST (Qualcomm Product Support Tools) version 2.7.496 or higher. Inside QPST is the QFIL executable.

Even with the correct Oppo R9s Plus Firmware Qfil file, you might encounter errors. Here is how to fix them:

This post explains how to flash stock firmware on the Oppo R9s Plus using QFIL (Qualcomm Flash Image Loader). Follow steps exactly — flashing firmware can brick your device if done incorrectly.