Did you read the e-mails you received regarding your interview? There are instructions regarding rescheduling towards the bottom.

"We understand that plans change. If you cannot interview at this time or no longer wish to be considered for a Delta Air Lines First Officer position, please reply to this email immediately. If it is less than three (3) business days, please call our Schedule Coordinators directly at ###-###-#### (redacted) to notify the team of the rescheduling or cancelation. This will allow us to offer this opportunity to a fellow candidate."