You can find tested Firehose loader files on several specialized firmware hosting sites:
If you choose the MSM Tool route, the Firehose is already included – you don’t need a separate download.
After flashing, unplug the USB cable. Hold the Power button for 15 seconds. The Oppo A3s should reboot to the setup screen.
Before you hit that download button, it is essential to understand what you are flashing.
Firehose is a tool used to flash or download firmware images to Android devices, including Oppo phones. It's typically used to unbrick or recover devices that have been bricked due to a faulty software update or other issues.