You don’t want to change the name of the element itself, so you want to leave the <h1> and </h1> as they are. You might want to reset the step to get the original HTML back.
The text for an element goes between the opening and closing tags for the element. So the text for an h1 element goes between the opening and closing h1 tags. At the beginning, the text for the h1 element is Hello World. You just want to change that text to CatPhotoApp.