Trever,
There are many methods to authentication with Zend Framework.
It could very well be through a config (config.ini / config.xml) or could be a part of one of your controllers, etc.
You may have to just take a look through the files to where it initializes the database connection.
I have a portion of MY code below (uses a config.ini)
$db = Zend_Db::factory($config->database);
and I have a config.ini (in application/config)
database.adapter = pdo_mysql
database.params.host = localhost
database.params.username = username
database.params.password = password
database.params.dbname = database
...
This is not hte only method of database connectivity but it may give you enough of an idea to find the vlaues you need to change.
Check your boostrap.php / index.php / initializer.php (AGAIN, depending on the chosen setup of Zend Framework).
If you follow index.php it will lead usually to some boostrap file (in my setups anyways).