Keychain does not preserve a log of old passwords.
The easiest path to recover access is usually requesting a password reset for the service involved.
If you are not using iCloud Keychain and do have local or iCloud backups, you could create another backup, restore the old backup, fetch the password, and then re-reset and restore the current backup. (When creating additional backups, avoid deleting the previous backup. That deletion is often the default.)
If the password is in iCloud Keychain, the password is gone from all connected devices. You might be able to recover it via a Mac and Time Machine sharing the same iCloud Keychain, maybe.