var container = FindNode<Control>("Lastground");
if (container != null)
{
    var model = container.GetNodeOrNull<Node>("Live2DTestModel");
    if (model != null)
        model.QueueFree();
}

var dragPanel = FindNode<Godot.ColorRect>("Live2DDragPanel");
if (dragPanel != null)
    dragPanel.QueueFree();