src/Settings.php
private function add($key, $value)
    {
        Yii::$app->db
            ->createCommand()
            ->insert($this->tableName, ['key' => $key, 'value' => $value])->execute();
    }
private function add($key, $value)
    {
        Yii::$app->db
            ->createCommand()
            ->insert($this->tableName, ['key' => $key, 'value' => $value])->execute();
    }
Add setting

@param string $key
@param string $value