2D car game touch control

Hi, I have a movement script for 2d car like this, and I don't know how to convert it from keyboard to mobile control. If someone can help me, I will be grateful :)

 using UnityEngine; 
 using System.Collections; 
 
 
 public class lJointCarMovement1 : MonoBehaviour { 
     //reference to the wheel joints
     WheelJoint2D[] wheelJoints; 
     //center of mass of the car
     public Transform centerOfMass;
     //reference tot he motor joint
     JointMotor2D motorBack;  
     //horizontal movement keyboard input
     float dir = 0f; 
     //input for rotation of the car
     float torqueDir = 0f;
     //max fwd speed which the car can move at
     public float maxFwdSpeed = -1500;
     //max bwd speed
     float maxBwdSpeed = 1500f;
     //the rate at which the car accelerates
     float accelerationRate = 1400;
     //the rate at which car decelerates
     float decelerationRate = -300;
     //how soon the car stops on braking
     float brakeSpeed = 2000f;
     //acceleration due to gravity
     float gravity = 9.81f;
     //angle in which the car is at wrt the ground
     float slope = 0;
     //reference to the wheels
     public Transform rearWheel;
     public Transform frontWheel;
     
     // Use this for <span id="IL_AD2" class="IL_AD">initialization</span> 
     void Start () { 
         //set the center of mass of the car
         GetComponent<Rigidbody2D>().centerOfMass = centerOfMass.transform.localPosition;
         //get the wheeljoint components
         wheelJoints = gameObject.GetComponents<WheelJoint2D>(); 
         //get the reference to the motor of rear wheels joint
         motorBack = wheelJoints[1].motor; 
     }  
     
     //all physics based assignment done here
     void FixedUpdate(){
         //add ability to rotate the car around its axis
         torqueDir = Input.GetAxis("Horizontal"); 
         if(torqueDir!=0){ 
             GetComponent<Rigidbody2D>().AddTorque(3*Mathf.PI*torqueDir, ForceMode2D.Force);
         } 
         else{
             GetComponent<Rigidbody2D>().AddTorque(0);
         }
         
         //determine the cars angle wrt the horizontal ground
         slope = transform.localEulerAngles.z;
         
         //convert the slope values greater than 180 to a negative value so as to add motor speed 
         //based on the slope angle
         if(slope>=180)
             slope = slope - 360;
         //horizontal movement input. same as torqueDir. Could have avoided it, but decided to 
         //use it since some of you might want to use the Vertical axis for the torqueDir
         dir = Input.GetAxis("Horizontal"); 
         
         //explained in the post in detail
         //check if there is any input from the user
         if(dir!=0)
             //add speed accordingly
             motorBack.motorSpeed = Mathf.Clamp(motorBack.motorSpeed -(dir*accelerationRate - gravity*Mathf.Sin((slope * Mathf.PI)/180)*80 )*Time.deltaTime, maxFwdSpeed, maxBwdSpeed);
         //if no input and car is moving forward or no input and car is stagnant and is on an inclined plane with negative slope
         if((dir==0 && motorBack.motorSpeed < 0 ) ||(dir==0 && motorBack.motorSpeed==0 && slope < 0)){
             //decelerate the car while adding the speed if the car is on an inclined plane
             motorBack.motorSpeed = Mathf.Clamp(motorBack.motorSpeed - (decelerationRate - gravity*Mathf.Sin((slope * Mathf.PI)/180)*80)*Time.deltaTime, maxFwdSpeed, 0);
         }
         //if no input and car is moving backward or no input and car is stagnant and is on an inclined plane with positive slope
         else if((dir==0 && motorBack.motorSpeed > 0 )||(dir==0 && motorBack.motorSpeed==0 && slope > 0)){
             //decelerate the car while adding the speed if the car is on an inclined plane
             motorBack.motorSpeed = Mathf.Clamp(motorBack.motorSpeed -(-decelerationRate - gravity*Mathf.Sin((slope * Mathf.PI)/180)*80)*Time.deltaTime, 0, maxBwdSpeed);
         }
         
         
         
         //apply brakes to the car
         if (Input.GetKey(KeyCode.Space) && motorBack.motorSpeed > 0){
             motorBack.motorSpeed = Mathf.Clamp(motorBack.motorSpeed - brakeSpeed*Time.deltaTime, 0, maxBwdSpeed); 
         }
         else if(Input.GetKey(KeyCode.Space) && motorBack.motorSpeed < 0){ 
             motorBack.motorSpeed = Mathf.Clamp(motorBack.motorSpeed + brakeSpeed*Time.deltaTime, maxFwdSpeed, 0);
         }
         //connect the motor to the joint
         wheelJoints[1].motor = motorBack; 
         
     }
     
 }