OK so obviously easiest thing to do here is ask the partner how they configured this, or review documentation they  provided, but I'm assuming you are here because those two things are not an option 🙂 

The field you are using, lets say 'Article Body' is a HTML field. As standard it comes with lots of formatting options including those Heading Styles.

As a first check, Right Click on the name of the field on the form, and click 'Configure Styles' and let's see if there is anything there first of all.