You must install the specific USB VCOM or ADB drivers for your chipset. Without these, the tool won't "see" your phone.
Ensure your device is charged to at least 50%. flashtool-v5.0.1
Click the (or Flash) button. Power off your device completely. While holding a specific key combo (usually Volume Down or Volume Up, depending on the brand), connect it to your PC. Step 4: The Flashing Process You must install the specific USB VCOM or