How to add extra html to the section id=”hero-header” on sensible theme?

I want to add an extra p tag to the <section id=”hero-header”> on the sensible theme…

But i dont know where.. im not so experieced with wp…

But i can code, i just need to know where to edit the file where the <section id=”hero-header”> is so i can add an extra p tag with some stuff..

Thanks.