<?php
 namespace VendorModuleController;
 class Save extends MagentoFrameworkAppActionAction
 {
public function __construct(
    MagentoSalesModelOrderItem $orderItem,
    MagentoFrameworkAppActionContext $context,
    MagentoFrameworkViewResultPageFactory $resultPageFactory
) {
    $this->orderItem = $orderItem;
    $this->result_page_factory = $resultPageFactory;
    parent::__construct($context);
}
public function execute()
{
    $orderId = 1;
    $order = $this->orderItem->getById($quote_id);
    $order->setCustomField('data you want to save');
    $order->save();
}}