Where to add form tips for custom fields in add listing?

Hi there

I’m using the classic coupon theme and have been updating the add listing form to make it easier to fill out as it can be confusing for members. I want to add instructions like what an offer is and take off the red * must-fill from the coupon code field, and a note about how to let me know their store name so I can add it to the store list. I’ve already updated some areas using the templates/add-form-details.php file but these particular ones are custom fields, and I can’t find the actual file to add my tips to. Can anyone point me in the right direction thanks?