How to set the default controller in yii2

Like few people already said, you need to add defaultRoute in the configurations file.
Here is how it should look:

//config/web.php in basic template or backend/config/main.php in advanced

$config = [
    ...
    'components' => [
        ...
    ],
    'params' => $params,
    'defaultRoute' => 'user/index',
];

Did you try in your config:

'defaultRoute' => 'user/index'

Default Controller