// require magento core
require_once 'app/Mage.php';

// execute on admin store
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);

$products = Mage::getModel('catalog/product')->getCollection();
foreach($products as $product) {
    echo $product->getName() . '<br/>';
    // save the product
    $product->save();
}

echo 'Congratulations!!! Product resaved';
?>

namespace SwiftOtterShareButtonsSetup;

use MagentoFrameworkAppState;
use MagentoCatalogModelResourceModelProductCollection;
use MagentoFrameworkSetup{UpgradeDataInterface, ModuleDataSetupInterface, ModuleContextInterface};

class UpgradeData implements UpgradeDataInterface
{
    protected $productCollection;
    protected $state;

    public function __construct(Collection $productCollection, State $state) {
        $this->productCollection = $productCollection;
        $this->state = $state;
    }

    public function upgrade(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
        $setup->startSetup();
        $this->state->setAreaCode('frontend');

        $products = $this->productCollection->load();
        $i = 0;

        foreach ($products as $product) {
            if ($i > 4) {
                break;
            }

            $product->save();
            $i++;
        }

        $setup->endSetup();
    }
}

<?xml version="1.0" ?>
<config>
    <module name="SwiftOtter_ShareButtons" setup_version="0.1.7" />
</config>

use MagentoFrameworkComponentComponentRegistrar;

ComponentRegistrar::register(ComponentRegistrar::MODULE, 'SwiftOtter_ShareButtons', __DIR__);

$objectManager = MagentoFrameworkAppObjectManager::getInstance();

$productCollection = $objectManager->create('MagentoCatalogModelResourceModelProductCollection');

$productCollection->load();

foreach($productCollection  as $product)
{

 ................

 ................

 ............

 $product->save();

}