Turn off your John Deere mower and wait for it to cool down before proceeding; remove the key from the ignition as well.
Lift the hood of your John Deere mower and locate the battery.
Use a wrench and the appropriate sized socket to remove the negative wire on the negative battery post.
Locate the reverse safety switch near the same side as the battery on your John Deere mower. There will be a plastic wire harness with wires. Grasp the wire harness and press down on the side tabs with your thumbs then pull them apart to unplug it.
Reconnect the negative battery lead onto the post then lower the hood on your John Deere mower. Insert the key in the ignition and operate as normally thereafter.