The top track in that setting is the Gradient media. Twirl this down (by clicking the triangle next to the name in the timeline) and you will see a track nested in the Mask track titled TEXT AS MASK. This is the text media track. Double click this and it will open the text editor, where you can edit this text. Once you have replaced the default text with the text that you want, close the text editor window and you should be good to go.