How can I change the instance of a prefab instead of the prefab itself?

I have a powerup (prefab) that changes the scale of a gameObject (prefab). However, my code is altering the prefab’s values and not the instance of the prefab.

public class WiderPowerUp : PowerUp
    [SerializeField] Paddle paddle; //Game Object being scaled

    protected override void TriggerPowerUp()
        Vector3 scale = paddle.gameObject.transform.localScale;
        scale.x += 0.1f;
        paddle.gameObject.transform.localScale = scale;

Is it possible to pass the local instance of a prefab to my script via [SerializeField], or do I have to use GameObject.Find()?

You can, but only if the gameobject is in the scene at the beginning already or (as far as I know) on editing the prefab (double click and make your references). But if your skript is on the gameobject you want, just use gameobject or for the transform transform for example: Vector3 scale = gameobject.transform.localScale; or even easier: Vector3 scale = transform.localScale;