Slider won't slide, issue assigning PlayerPrefs and then changing the PlayerPrefs' value

I am new to Unity and am trying to create a Pong game with some additional features, such as changing the players' speed. The slider I created and player are in different scenes so to go around this I used the following piece of code:

 public class PlayerSpeed : MonoBehaviour {
 
     public Slider PSlider;
     float speed;
 
     public void ChangePlayerSpeed(Slider PSlider){
         speed = PlayerPrefs.GetFloat("Speed", 0);
         PSlider.value = speed;
     }
 }

I am certain my issue is in this bit of code as I can change the slider value to another number in the Inspector, but once I try to slide the value, it changes to the value I assigned in PlayerPrefs.SetFloat. Though maybe the issue is in the other piece of code for the actual movement speed as I then again use PlayerPrefs.GetFloat, rather than the newly assigned speed. public class PlayerControls : MonoBehaviour {

     public KeyCode moveUp = KeyCode.W;
     public KeyCode moveDown = KeyCode.S;
     float speed;
     public float boundY = 2.25f;
     private Rigidbody2D rb2d;
 
 
     void Start () {
         rb2d = GetComponent<Rigidbody2D> ();
         speed = PlayerPrefs.GetFloat("Speed", 0);
     }
 
     void Update () {
         var vel = rb2d.velocity;
         if (Input.GetKey (moveUp)) {
             vel.y = speed;
         } else if (Input.GetKey (moveDown)) {
             vel.y = -speed;
         } else if (!Input.anyKey) {
             vel.y = 0;
         }
 }

Any help will be appreciated, been stuck on trying to get this slider to change the speed for hours.