you must retrieve a special access code from your contact email. However, you may deactivate this setting, and this article will show you how. To disable the Steam guard mobile authenticator security ...

The Steam Guard Code changes every thrity seconds and ... accessing the Steam Guard Menu at the top, and selecting "Remove Authenticator". This brings up a window where you can confirm that ...

I no longer have access to my Mobile Authenticator codes. From there, tap Remove authenticator in order to delete Steam Guard from the older device. You will see some additional instructions.