you need to log into your SE account (not ffxiv) here: https://secure.square-enix.com. once logged in under "services and options" you should see "one-time password". if you not written down the emergency password at this point, do that now just to be safe. but click on the type of key in use currently and on the next screen you should see the button for removing the key from your account. the emergency key is good to have in a safe spot in case the physical key, if used, dies or is lost but also for the software token in case you lose access to that as well.