Доступ до FirstPersonController

using System.Collections;

using System.Collections.Generic;

using UnityEngine;

using UnityStandardAssets.Characters.FirstPerson;

public class SpeedChange : MonoBehaviour

{

    public GameObject p;

    RigidbodyFirstPersonController script;

    void Start()

    {

       script = p.GetComponent<RigidbodyFirstPersonController>(); 

    }

    void Update()

    {

        print(script.movementSettings.ForwardSpeed);

        if (Input.GetKeyDown(KeyCode.R))

        {

            script.movementSettings.ForwardSpeed *= 2;

        }

    }

}

FirstPersonController - для доступу треба зробити відповідне поле публічним