How Do I Increase the ForwardForce of the player over time? using rigid body

Hello,
I am trying to increase the forward force of the player when a milestone is set, that each time the x- axis is increased the more forward force the player will receive. I have also a score that shows how far the player is on the X-axis.

using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
public Rigidbody rb;

public float forwardForce = 2000f;
public float slidewaysForce = 500f;
public float upwardForce = 10f;

// Update is called once per frame
void FixedUpdate()
{
    rb.AddForce(0, 0, forwardForce * Time.deltaTime);
    
    if (Input.GetKey("d"))
    {
        rb.AddForce(slidewaysForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);

    }
    if (Input.GetKey("a"))
    {
        rb.AddForce (-slidewaysForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);
    }
    if (Input.GetKey("w"))
    {
        rb.AddForce (0, upwardForce * Time.deltaTime, 0, ForceMode.VelocityChange);
    }
    if (Input.GetKey("s"))
    {
        rb.AddForce(0, -upwardForce * Time.deltaTime, 0, ForceMode.VelocityChange);
    }
        
    if (rb.position.y < -1f)
    {
        FindObjectOfType<GamerManager>().EndGame();
    }
        
}

}

void Update(){
if(gameObject.transform.position.x > milestone)
{
forwardForce+=10;
milestone += milestoneIncremtDistance;
}
}
Long story short, this increases your forward force, every time you travel 1 milestoneIncremtDistance.

you can use GetKeyDown instead, you may have to decrease the force and or add more drag to the rigidbody