You can find the specific CPH1803 QFIL firmware on Evilicacell.
: Essential for the PC to recognize the device in EDL (Emergency Download) Mode . 2. Enter EDL Mode (9008 Mode) oppo a3s qfil firmware cph1803 qfil flash file link
The Oppo A3s uses a Qualcomm chipset, which makes the appropriate low-level flashing tool for restoring the device when it is hard-bricked, stuck in EDL (Emergency Download Mode), or suffering from critical software corruption. You can find the specific CPH1803 QFIL firmware