How to convert "SpriteRenderer" command to "TilemapRenderer" command?

I’m having a little trouble finding help on Google to add new features to the game. The game will have a hidden area, when the “Player” performs a “Trigger” that area will remove the overlay that hides that area.

The problem is that their command uses “SpriteRenderer” rendering while I’m using “TilemapRenderer”. So how to convert “SpriteRenderer” command to “TilemapRenderer” command?

    public SpriteRenderer[] wallElements;
    public float disappearRate = 1f;
    float alphaValue = 1f;
    bool playerEntered = false;
    public bool toggleWall = false;

    void Update()
            alphaValue -= Time.deltaTime * disappearRate;

            if(alphaValue <= 0){
                alphaValue = 0;

            foreach(SpriteRenderer wallItem in wallElements){
                wallItem.color = new Color(wallItem.color.r, wallItem.color.g, wallItem.color.b, alphaValue);

Does not seem to able to do on the tilemapRenderer, but since you have a tilemapRenderer I’m guessing you have a tilemap-component as well on the gameobject.
And tilemap has a color-variable, on which you can set the alpha.