This is site-specific, but typically by using the same mechanisms used to reset forgotten passwords.
Also, sites can and often do support multiple passkeys, which opens up the possibility of allowing for reliable account recovery using one or more backup devices (one or more YubiKeys, for instance) that is still siginificantly more secure than reset flows using SMS or email.
Also, sites can and often do support multiple passkeys, which opens up the possibility of allowing for reliable account recovery using one or more backup devices (one or more YubiKeys, for instance) that is still siginificantly more secure than reset flows using SMS or email.