Rigidbody.velocity control the speed and slow down the speed with mobile platform input Like Button Handle

Rigidbody.velocity control the speed and slow down the speed, And with mobile platform input Like "Jump" button.

I would like the say, like when the ball is falling at the high way, and u press "Slow" then will slow down the ball. And the other word u press the 'speed' it will speed up the ball is falling

I hope some answer me is the (Mobile platform input Like Button Handle)

please i need the best answer and I found this one but it not work for the mobile setting platform input

 var Speed: float = 0; //Don't touch this 
  var MaxSpeed : float = 10;//This is the maximum speed that the object will achieve 
  var Acceleration : float = 10;//How fast will object reach a maximum speed 
  var Deceleration : float = 10;//How fast will object reach a speed of 0
  
  function Update() {
      if ((Input.GetKey("left")) && (Speed < MaxSpeed)) 
      Speed = Speed - Acceleration * Time.deltaTime;
      else if ((Input.GetKey("right")) && (Speed > -MaxSpeed))
          Speed = Speed + Acceleration * Time.deltaTime;
      else {
          if (Speed > Deceleration Time.deltaTime) 
          Speed = Speed - Deceleration * Time.deltaTime;
          else if (Speed < -Deceleration Time.deltaTime) 
              Speed = Speed + Deceleration * Time.deltaTime;
          else Speed = 0;
      }
      transform.position.x = transform.position.x + Speed * Time.deltaTime;
  }

and i cannot function the, **transform.position.x = transform.position.x + Speed Time.deltaTime;*