There's a small room that's labeled as "Office" with a giant mole inside. So anyway, when you start the dungeon there will be an encounter with some moles that will ask you what kind of worker you are cause you're new (if I remember correctly) , just choose the option that you are a "sus" one and then keep moving on from then til you reach the office to get your work permit registered.
You know you are one when the supervisor mole takes you to some private do some "alone time" with him but then got interrupted.