$objectManager = MagentoFrameworkAppObjectManager::getInstance();
    $resource = $objectManager->get('MagentoFrameworkAppResourceConnection');
    $connection = $resource->getConnection();
    $sqlx = "SELECT * FROM sales_order ORDER BY entity_id DESC LIMIT 1";
    $connection->query($sqlx);
    $resultx = $connection->fetchAll($sqlx);
    foreach($resultx as $resulx) { $entityid  = $resulx['entity_id']; }
    $sql = "SELECT * FROM sales_order_item WHERE order_id='$entityid'";
    $connection->query($sql);
    $results = $connection->fetchAll($sql);
    foreach($results as $result)
    {
        $item_id = $result['item_id'];
        $fullopt = $result['product_options'];
        $needle = 'Shoe Size';
        if (strpos($fullopt, $needle) !== false){
            $pieces = explode('Shoe Size","value":"', $fullopt);
            $sizenum = explode('","option_id', $pieces[1]);
            if(strpos($fullopt, '"value":"EU"') !== false) {
                $rsizenum1 = $sizenum[0]+31;
                $finalque = $pieces[0].'Shoe Size","value":"'.$rsizenum1.'","option_id'.$sizenum[1];
            }
            else if(strpos($fullopt, '"value":"UK"') !== false) {
                $rsizenum2 = $sizenum[0]-1;
                $finalque = $pieces[0].'Shoe Size","value":"'.$rsizenum2.'","option_id'.$sizenum[1];
            }
            else{
                $finalque = $fullopt;
            }
            $upsql = "UPDATE sales_order_item SET product_options='$finalque' WHERE item_id='$item_id'";
            $connection->query($upsql);
        }
    }