Souke/backend/forms/UserImportUploadForm.php

<?php

namespace backend\forms;

use yii\base\Model;
use yii\web\UploadedFile;

class UserImportUploadForm extends Model
{
    /**
     * @var UploadedFile file attribute
     */
    public $file;

    /**
     * @return array the validation rules.
     */
    public function rules()
    {
        return [
            [['file'], 'file', 'skipOnEmpty' => false, 'mimeTypes' => 'text/csv, text/plain'],
        ];
    }

    public function attributeLabels()
    {
        return [
            'file' => "Fichier d'import (CSV)"
        ];
    }
}

?>