Player Controller "Horizontal" input convert to "left" and "right"

I am currently creating a game in which the player can drive around on a spherical planet. I wrote the code below with original intentions of publishing it on a pc platform but I decided to convert it over to mobile. What I would like to do is convert what is in the fixed update into two separate voids: a left control and a right control (idk if that makes sense). I guess what I am trying to say is how would I convert

rotation = Input.GetAxisRaw("Horizontal");

into a left and right void? Thanks

 public float rotateInBetween = 4f;
 public float rotateAdd = 25f;
 public float moveSpeed = 5f;
 public float rotationSpeed = 200f;
 public float accelerationAddSpeed = 0f;
 public float accelerationInBetween = 0f;
 public float slowMotionLength = 3f;
 public float animationSlow = .2f;

 private float rotation;
 private Rigidbody rb;

 void Start()
 {
     rb = GetComponent<Rigidbody>();
     StartCoroutine(rotateSpeedAdd());
 }

 void Update()
 {
     if (Input.GetButtonDown("Fire1"))
     {
         StartCoroutine(timeSlowPowerUp());
     }

     rotation = Input.GetAxisRaw("Horizontal");
     rotateSpeedAdd();
 }


 void FixedUpdate()
 {
     rb.MovePosition(rb.position + transform.forward * moveSpeed * Time.fixedDeltaTime);
     Vector3 yRotation = Vector3.up * rotation * rotationSpeed * Time.fixedDeltaTime;
     Quaternion deltaRotation = Quaternion.Euler(yRotation);
     Quaternion targetRotation = rb.rotation * deltaRotation;
     rb.MoveRotation(Quaternion.Slerp(rb.rotation, targetRotation, 50f * Time.deltaTime));
     //transform.Rotate(0f, rotation * rotationSpeed * Time.fixedDeltaTime, 0f, Space.Self);
 }