Your email address is in your account settings. Change it there, then open the confirmation sent to the new address — until you do, the old address is still the one that works, which is deliberate. It stops somebody who gets hold of your session from quietly moving your account somewhere you cannot reach it.
Everything moves with the change: your appointments, your Beauty Passport, your saved professionals, your message threads. It is the same account with a new address on it, not a new account.
Your email address is also how you sign in, so use the new one from then on. If the confirmation does not arrive within a few minutes, check the spam folder before trying again — a second attempt invalidates the first link.
If you have lost access to the old address entirely and cannot sign in at all, use the password reset on the address you can still reach, or contact us if neither address works.