It's easy to delete a pass that was mistakenly assigned to a customer. Just go to the customer's Overview tab, and click on the dots for more options in the top right of the pass. Simply delete the pass from there:
If a pass has attendances on it already, you can't delete the pass without first removing the attendances from that pass. Here's how to remove past attendances from a person's pass.
If the pass was purchased via Stripe, you can process a refund via Punchpass. Here's how.