Generate Tiles Programatically Over Player Position?

I'm working on a basic 2D top-down game using Unity and have a player sprite that I move using the directional arrow keys.

This player sprite (a unicorn) is on a tilemap.

How do I generate tiles (rainbow tile) where ever my unicorn moves along the tilemap?

I read the manual from Unity saying that there's a Tile class that I can use to do it: https://docs.unity3d.com/Manual/Tilemap-ScriptableTiles-Tile.html but I'm still a bit perplexed on how to actually implement it.

I have a Player Collision script that goes:

 public class UnicornCollision : MonoBehaviour {
 
    public void OnTriggerEnter2D(Collider2D other){
 
       if (other.gameObject.tag.Equals("SpaceTile")
       {
           Debug.Log("You're on a space tile");
 
           // Insert code to generate rainbow tiles here.
       }
 
       else if (other.gameObject.tag.Equals("GrassTile")
       {
           Debug.Log("You're on a grass tile");
       }
 
    }    
 }

And I have 2 tilemaps each tagged with "SpaceTile" or "GrassTile" as well as each having a Tilemap Collider 2D to detect collision on trigger.

My unicorn sprite (player) has a Rigidbody 2D and Polygon Collider 2D components.