Controlling a RC Car by connecting BOLT to Arduino

I am trying to control a car by connecting IOT BOLT to Arduino. For this I need to send a character to BOLT via internet and BOLT sends this to Arduino . The Arduino code is working fine but it is not receiving the right character from BOLT.
I wrote the following code to send a character to BOLT. F makes the car go forward and S makes the car stop.

     <button onclick="serialWrite?data='F'" >FORWARD</button>
     <button onclick="serialWrite?data='S'">STOP</button>


I do not understand how to use the controller.js file. How do I link two files to the device?

Is the code is correct

I don’t know. That’s why I am asking . This code doesn’t send the characters I want to send to Arduino.