Sorry for the late reply, I didn’t notice this in my inbox. Are you still having an issue or did you move on?
When we setup the email section if I clicked the “forgot password” it gave me the same message as you, but I also got an email in my inbox with a one-off reset link. This could be because we have LDAP setup and it checks the email field of the user object…
Might be out of luck that way, but I did see some posts on here about going into the h2 DB that metabase stores settings in and resetting it that way.
EDIT: found one How do you reset a user's password without an email service configured or admin access?