Getting back in when the usual route is unavailable.
Ten are issued when the account is first set up. Each works once. They are the only route that does not depend on a device you still have, which is exactly why they need to be somewhere you can reach without that device — a password manager on another machine, or paper.
Choose the recovery option at sign-in and enter the code. It is consumed on use whether or not the sign-in completes, so do not re-enter the same one.
A fresh set can be generated from an active session, which invalidates any unused codes from the previous set. Generate a new set once you are down to two.
This needs a person. Contact whoever administers the account — there is no self-service route, by design.
Account help