How to transform PC controls to Touchscreen controls

So here is the moving forward script for PC:

wheelRR.motorTorque = maxTorque * Input.GetAxis("Vertical");
wheelRL.motorTorque = maxTorque * Input.GetAxis("Vertical");

And the touchscreen (Android) button:

if (touch.phase == TouchPhase.Stationary && gasButton.HitTest (touch.position)) {
    			//how should i type the moving forward script here to work? 

why do i need this? because i have a lot of scripts for carcontrol, but they work on PC, how to make them for Android?

how to make all this for Android?

as you can see from the documentation Input.GetAxis is passing float between -1 to 1.
so calculate this value from your touch location and pass it to the wheelRR.motorTorque with variable.