Obtain a replacement emblem of the same or similar material as the old one. This is so if the air bag deploys, it will break the seal and cause less harm to the driver. Do not try to remove the original emblem. Even if it is damaged or scratched, you wont be able to remove it without replacing the air bag as well.
Apply an adhesive to the back of the replacement emblem.
Align and place the replacement emblem over the old one. Hold it for a few minutes to make sure it sticks properly.