Default selection in Select Field

Ok here is the situation. We have a sign up form for our conference and one of the questions is a select type. It asks them to pick their sales rep. We have had a couple people just pass the required question and leave it as the top choice which is the wrong rep. Am I able to default it to some kind of option such as blank where they are forced to make a choice instead of being able to just continue on?

Sorry if this is a bit wordy. I was unsure of how to word this question.

https://wordpress.org/plugins/visual-form-builder/