Hard reset for Oppo A3S:

 Here's how you can perform a hard reset on your Oppo A3S:

Step 1: Power-Off your device and make sure that the battery is charged at least up to 50%.

Step 2: Simultaneously press and hold "volume down" + "Power" keys until the Oppo logo appears on your screen.

Step 3: You won't be able to use the touchscreen at this point. So, use the volume keys to navigate to the "Wipe Data/Factory Reset" option. Now, press the "power" key to initiate the hard-reset process.

Once the reset process completes, you'll be welcomed by the FRP login window, which might cause trouble as well.