Strip 1 or 2 inches of rubber shielding from the end of your cable using the wire stipper. Be careful not to cut into the inner wires.
Separate the three internal wires. Two of these should be shielded red and black wires, and the third is most often a bare wire. Strip 1/4 inch of shielding from each of these inner wires.
Disassemble the XLR connector by removing the small screw with a Phillips-head screwdriver. Slide the inner connector from its outer casing. You should see three small contacts on the inner side of the connector, which are labeled 1, 2 and 3.
Prepare the three wires of the cable by applying a small amount of solder to the tip of each one.
Solder the bare wire to the number 1 contact of the XLR connector. Solder the red and black wires to the number 2 and 3 contacts respectively.
Allow the connector and cable to cool for several minutes. Place the connector back into it's casing (a small notch in the casing ensures it can only fit in one position), and secure again it using the small screw.