My 2 'sense' .... one should always have at least 2 accounts set to admin levels in moodle that authenticate as manual. Why? IF SSO/alt logins/external DB/or student info system or whatever is being used for teachers/students has issues, no one can login to the moodle.
Now if your entity has had moodle a long time, admin of the moodle may have changed hands and none know of a manual account. The initial installer of the moodle had to set up an admin level account. That user ID number is 2.
Query mdl_user table like so:
select id,username,email from mdl_user where id='2';
The password is md5hashed so you can't use what you see in the DB when attempting to use that, but, if none know the password, it can be changed by using moodlecode/admin/cli/reset_password.php.
This shared from past experiences. ;)
'SoS', Ken