The firehose file (typically ending in .mbn or .elf ) acts as a bridge. For the Oppo A3s, which runs on the chipset, this file tells flashing tools like QFIL or UnlockTool how to write data to the device's partitions. Essential Download Links
The Ultimate Guide to Downloading and Using Firehose Programmer File for Oppo A3s (CPH1803) download firehose oppo a3s cph1803