No need to make changes at all. If you have setup your database connetion you will be able to use:
$this->db->query('SELECT.....');
In my case the DB service is named 'db', but you can change it to anything you want:
// Database connection
$di->set('db', function() use ($config) {
return new \Phalcon\Db\Adapter\Pdo\Mysql([
'host' => $config->host,
'username' => $config->username,
'password' => $config->password,
'dbname' => $config->name,
'charset' => 'utf8',
'options' => [
\PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
\PDO::ATTR_PERSISTENT => true,
\PDO::ATTR_STRINGIFY_FETCHES => false
]
]);
});