How do i move a 3D ball along the z-axis?

Hello there, I have a game in which you are a ball from the first person perspective. You can roll along the x-axis with w and s. I also want to move the ball along the z-axis with the a and d keys but i can’t figure out how. I have tried many thing and looked at a lot of scripts but nothing worked. I hope one of you can help me.

Please any tips or hints would be amazing. Thank you in advance.

*update
I edited the script to:

#pragma strict

var rotationSpeed = 100;
var jumpheight = 8;	
	

private var isFalling = false;

function Update () 
{
	
   var rotation : float = Input.GetAxis ("Horizontal") * rotationSpeed;
    rotation *= Time.deltaTime;
    rigidbody.AddRelativeTorque (Vector3.left * rotation);
   var rotation2 : float = Input.GetAxis ("Vertical") * rotationSpeed;
   rotation2 *= Time.deltaTime;
   rigidbody.AddRelativeTorque (Vector3.back *rotation2);
  

 if (Input.GetKey(KeyCode.Space)  && isFalling == false)
   {
   		rigidbody.velocity.y = jumpheight;
   }
   		isFalling = true;
}	

function OnCollisionStay ()
{
	isFalling = false;
}

And now it works thanks guys :smiley:

Just as Graham Dunnett :diamonds::diamonds: stated.

add 3 more lines next to this:

var rotation : float = Input.GetAxis ("Vertical") * rotationSpeed;
rotation *= Time.deltaTime;
rigidbody.AddRelativeTorque (Vector3.back * rotation); 

looking like this:

var rotation : float = Input.GetAxis ("Horizontal") * rotationSpeed;
    rotation *= Time.deltaTime;
    rigidbody.AddRelativeTorque (Vector3.left * rotation); 

And by the way, you are moving on the Z axis with your W/S, and now will be able to move on the X with A/D. This is because Vector3.back stands for Vector3(0, 0, -1), which goes like (X, Y, Z). See Vector3 Documentation for more info.