Now some of you won't have been to Park Hill before , so let me explain about our facility
would you please explain how the writer used future perfect with " before "
That won't does not signify futurity: it's an 'epistemic' use of will to signify inferential certainty. Compare:
A: Mom, there's somebody in the garage.
B: Oh, that will be the boy I hired to mow the lawn.
In paraphrase, the speaker is saying
I'm sure there are some of you who haven't been here before.