These instructions take for granted how the battery itself should be replaced. I imagine you reconnect the contact with the red wire to the positive side of the CR2032 battery and the contact for the black wire to the negative and wrap electrical tape around the entire thing BEFORE reconnecting it and then following these instructions in reverse order.

This does not explain how to get the battery out of the black plastic, replace it, and put the wires back. That's the most important part!