How do I revoke access from a lost or someone else's device?
In your account on the website, in the devices section, tap “Revoke” next to the entry. Access stops immediately, and the device is signed out at its next connection.
Revoking affects only that device: your other phones and your active session on the website keep working.
If the phone is lost, also change your password — this closes all active sign-in sessions on the website too. The list of sessions is in the security section of your account.