If you chose a different format or if you still want to return the Kindle format, contact OverDrive directly using their support form, requesting that they reset the checkout on that particular item so you can choose the correct format.
You should receive a response by email within 8 business hours of receipt or within 24 hours if received outside of their regular business hours (8:30 am – 5:30 pm ET Monday-Friday, excluding major holidays).