It isn’t described anywhere. Soo probably a password reset by email

It’s a solution that was long overdue, but they didn’t account for multiple devices and application.

It’s pretty shit tbh. Was looking forward to using it, but I’ll stick with random characters

You can't because the certs are on the device in a secure enclave. Unless you let Google/apple/Microsoft back them up to their cloud. Then you need to hope you don't lose access to that too when you're device was lost. Or you can just have multiple devices/security keys in case this happens.