Once you have located the fuse box, find the relay labeled "Rear Wiper." It is a small, black box with a metal connector. The relay should be located in slot #17 in the fuse box. To remove the relay, simply pull it straight out of the socket.
If you are replacing the rear wiper relay, make sure to purchase a relay that is compatible with your car. You can find the part number for the correct relay in your car's owner's manual.