I'm using the [enewsletter_subscribe] shortcode but need

Hello, I'm using the [enewsletter_subscribe] shortcode but need to find a way to customize it to add some text to explain what it is people are subscribing to.

My developer has customized the CSS box as you can see on this page:
http://lsi.io

However, I don't see any way to add text in this subscribe box...

Thank you for your assistance.