how to select/change which sprite set is used from a multiple set spritesheet?

how to select/change which sprite set is used from a multiple set spritesheet?

game simple : Muffin Knight Gameplay Trailer - YouTube

This is what works for me in this scenario. This way you can get all the Sprites inside the single Texture., First, you will need to get a “Resource” folder inside the “Asset” folder (Note: Anything within the Resource folder can be gathered within the script).
Here is an example using

    public class CursorScript : MonoBehaviour
    {
        private SpriteRenderer spriteRender;
    
        private Sprite[] renderToSprite;
    
        // Start is called before the first frame update
        void Start()
        {
            //Get the "SpriteRender Component to modified the image of the cursor.
            spriteRender = gameObject.GetComponent<SpriteRenderer>();
    
            //Set the name of the Image Sprite.
            string multiSpriteName = spriteRender.sprite.texture.name;
    
            //Set the location A.K.A the path of where the multi-Sprite Image is located 
(Note: The image has to be inside the "Resource" Folder).
            string path = "Sprites/UI/";
    
            //Get all Sprites that fit the requirements to cast into the "RenderToSprite".
            renderToSprite = Resources.LoadAll<Sprite>(path + multiSpriteName);
    
            //Render a new sprite selected in the "renderToSprite[Array]".
            spriteRender.sprite = renderToSprite[1];
    
        }
    }

This is what works for me in this scenario. This way you can get all the Sprites inside the single Texture.