Reschedule your time right away!
Don't wait too long. You have a better chance of rescheduling the hearing if you ask before the hearing, not after.
If you will be representing yourself at a hearing, call the agency and ask them to reschedule your hearing.
If you will be representing yourself in a court proceeding, call the clerk's office and ask them how to get a continuance in your case. A continuance means that you are asking for a later court date.