That's a good one!
Let's see, an appointment without an appointment? I assume you would like to have a walk in visit? If so, then call the office and see if they accept walk-ins.
If so, bingo! otherwise you wold need to go to a "walk-in" clinic or urgent care
center. Many offices have same day appointments and will accept walk=ins. It may require an uncomplicated complaint and cash or verifiable insurance