I cannot find the serial number. How can I make an appt to bring it in

If you have an Apple ID associated with the device, log in at Apple ID account website and list the devices for that account, find your Mac, and select it to show the serial number.

If you don't have an Apple ID for the device, if you still have the purchase receipt or box that it came in, the serial number will be on those.

Turn it over. The serial number should be etched on the bottom.