Editing multiple layers set up with buttons

I am new to Storyline 360 and have the task of editing some previousy created templates.

I am having trouble accessing a layer that is set up for access by buttons on the presentation. I can access the main slide text and the first level of buttons text from the "Slide Layers" list on the bottom right corner of the page. However, the next level/layer, which is accessed by additional buttons, does not show up under "Slide Layers", so I can't access the text of those button layers for editing. Can anyone help?