If they aren't familiar with a specific benefit, just ask for what you would want. Do you most want a free drink, free appetizer, desert, what is it? Just tell them that is what you usually get as a result of the Chef's Taste or the secret word. You must do this in both a confident and respectful way. If you wallow or are not confident you are not going to get what you want in many cases. You should phrase it like its a given, no big deal!

There is some concept in psychology that your confidence in getting something is very important in terms of whether you will get it.