The selected answer doesn't consider MSI. in order to avoid generation a salable qty issue. You could also add this code, 

`public function fixReservationForUncancel(String $incrementId, String $sku, int $qty){

        /** @var \Magento\Framework\ObjectManagerInterface $objectManager */
        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();

        /** @var Magento\Framework\App\ResourceConnection $resourceConnection */
        $resourceConnection = $objectManager->create(\Magento\Framework\App\ResourceConnection::class);

        $connection = $resourceConnection->getConnection();
        $tableName = $resourceConnection->getTableName('inventory_reservation');

        $insertQuerry= [
            'stock_id' => 1,//Check your stock id in the same reservation table
            'sku' => $sku,
            'quantity' => $qty*-1,
            'metadata' => '{"event_type":"order_uncancel","object_type":"order","object_id":"","object_increment_id":"'. $incrementId .'"}'
        ];
        
        $qry= $connection->insert($tableName, $insertQuerry);

    }`