Add action to controller:

    public function actionClone($id)
    {
        // set to 'false' to overcome 'Unable to verify your data submission: 
        // Bad request (#400)' error.
        $this->enableCsrfValidation = false;  
 
        $model = $this->findModel($id);
 
        // Copy data (except ID)
        $dataCopy = $model->attributes;
        unset($dataCopy['id']);  // to insert new record with a copy of the data
        $dataCopy['company_name'] = $dataCopy['company_name'] . ' (Copy)';
        $newModel = new Distributor();
        $newModel->setAttributes($dataCopy, false);
 
        if ($newModel->save()) {
            Yii::$app->session->setFlash('success', "Successfully cloned Distributor.");
            return $this->redirect(['update', 'id' => $newModel->id]);
        } else {
            // Could not save copy, so we simply view original record
            Yii::$app->session->setFlash('error', "Failed to clone Distributor.");
            return $this->redirect(['view', 'id' => $model->id]);
        }
 
        $this->enableCsrfValidation = true;  // restore CSRF validation
    }

Add button to View view:

  <?= Html::a('<i class="fa fa-clone" aria-hidden="true"></i>' . Yii::t('app', 'Clone'),  
      ['clone', 'id' => $model->id], ['class' => 'btn btn-default']) 
  ?>

Add button to Index view:

    <?= GridView::widget([
        'dataProvider' => $dataProvider,
        'filterModel' => $searchModel,
        'columns' => [
            ['class' => 'yii\grid\SerialColumn'],
 
            'id',
            //...
 
            //['class' => 'yii\grid\ActionColumn'],
            [  // custom actions
               'class'    => 'yii\grid\ActionColumn', 
               'template' => '{view} {update} {delete} {clone}', /* '{view} {update} {delete}' */
               'buttons'  => [
                   'clone' => function ($url, $model, $key) {
                       return Html::a('<i class="fa fa-clone" aria-hidden="true"></i>',
                           yii\helpers\Url::toRoute(['clone', 'id' => $model['id']])  // clone record
                       );  
                   },
               ],
            ],
        ],
    ]); ?>