How can I add sprint function into my Script?

The increase speed float is sprint but how can i add the sprint into my fixedupdate??

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MovementController : MonoBehaviour
{
    public float movementSpeed = 3f;
    public float IncreaseSpeed = 6f;
    public float rotationSpeed = 90f;

    public float cameraDistance = 5f;
    public float cameraHeight = 10f;

    Transform mainCamera;
    Vector3 cameraOffset;

    void Start()
    {
        cameraOffset = new Vector3(0f, cameraHeight, -cameraDistance);

        mainCamera = Camera.main.transform;
        MoveCamera();
    }

    void  FixedUpdate()
    {
        float rotation = Input.GetAxis("Horizontal");
        float movement = Input.GetAxis("Vertical");

        GetComponent<Rigidbody>().velocity = transform.forward * movementSpeed * movement;

        transform.Rotate(Vector3.up * rotationSpeed * rotation * Time.deltaTime);

        MoveCamera();
    }

    void MoveCamera()
    {
        mainCamera.position = transform.position;
        mainCamera.rotation = transform.rotation;
        mainCamera.Translate(cameraOffset);
        mainCamera.LookAt(transform);
    }
}

I would just add a while loop using whatever input you want the sprint to be associated with, i like left shift as my sprint, then set the velocity to your sprint speed.

while (Input.GetKey(KeyCode.LeftShift))
{
GetComponent().velocity = transform.forward * increaseSpeed* movement;
}

You may also have to add an if statement for setting the speed back to normal if it doesnt automatically

if (Input.GetKeyUp(KeyCode.LeftShift))
{
GetComponent().velocity = transform.forward * movementSpeed * movement;
}