Look at the bottom of the tool's window. It should say or "Found One MASKROM Device" .
Flashing the wrong firmware will hard-brick your device. Ensure the firmware matches your specific board model. Rk Android Tool V2.7.1
You must install the official Rockchip DriverAssitant on your Windows PC. Look at the bottom of the tool's window
You are trying to flash firmware meant for a different Rockchip processor (e.g., flashing RK3399 firmware onto an RK3288 device). Rk Android Tool V2.7.1
Hold down the physical or Recovery button on the device.