The Oppo F1s was released in mid-2016 as a "Selfie Expert" mid-range device. Technically, there are two main variants regarding hardware:
Only works if you have stock recovery and an official update zip. Oppo F1s Mt6755 Firmware
Originally Android 5.1 (Lollipop) with ColorOS 3.0; upgradable to Android 6.0 (Marshmallow) Official Support: The Oppo F1s was released in mid-2016 as
Modifying firmware voids your warranty and risks permanent damage. The author assumes no liability for bricked devices or lost IMEI data. Proceed at your own risk. Oppo F1s Mt6755 Firmware
If you need to revive a bricked unit: is your only reliable path.