Check how it's done in the \Magento\Sales\Block\Order\Items::_prepareLayout() method. You create item collection factory and use it as collection for building pager

    /**
     * @param \Magento\Framework\View\Element\Template\Context $context
     * @param \Magento\Framework\Registry $registry
     * @param array $data
     * @param \Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory|null $itemCollectionFactory
     */
    public function __construct(
        \Magento\Framework\View\Element\Template\Context $context,
        \Magento\Framework\Registry $registry,
        array $data = [],
        \Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory $itemCollectionFactory = null
    ) {
        $this->_coreRegistry = $registry;
        $this->itemCollectionFactory = $itemCollectionFactory ?: \Magento\Framework\App\ObjectManager::getInstance()
            ->get(\Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory::class);
        parent::__construct($context, $data);
    }

    /**
     * Init pager block and item collection with page size and current page number.
     *
     * @return $this
     */
    protected function _prepareLayout()
    {
        $this->itemsPerPage = $this->_scopeConfig->getValue('sales/orders/items_per_page');

        $this->itemCollection = $this->itemCollectionFactory->create();
        $this->itemCollection->setOrderFilter($this->getOrder());
        $this->itemCollection->filterByParent(null);

        /** @var \Magento\Theme\Block\Html\Pager $pagerBlock */
        $pagerBlock = $this->getChildBlock('sales_order_item_pager');
        if ($pagerBlock) {
            $pagerBlock->setLimit($this->itemsPerPage);
            //here pager updates collection parameters
            $pagerBlock->setCollection($this->itemCollection);
            $pagerBlock->setAvailableLimit([$this->itemsPerPage]);
            $pagerBlock->setShowAmounts($this->isPagerDisplayed());
        }

        return parent::_prepareLayout();
    }

Check how it's done in the \Magento\Sales\Block\Order\Items::_prepareLayout() method.

You create item collection factory and use it as collection for building pager

    /**
     * @param \Magento\Framework\View\Element\Template\Context $context
     * @param \Magento\Framework\Registry $registry
     * @param array $data
     * @param \Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory|null $itemCollectionFactory
     */
    public function __construct(
        \Magento\Framework\View\Element\Template\Context $context,
        \Magento\Framework\Registry $registry,
        array $data = [],
        \Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory $itemCollectionFactory = null
    ) {
        $this->_coreRegistry = $registry;
        $this->itemCollectionFactory = $itemCollectionFactory ?: \Magento\Framework\App\ObjectManager::getInstance()
            ->get(\Magento\Sales\Model\ResourceModel\Order\Item\CollectionFactory::class);
        parent::__construct($context, $data);
    }

    /**
     * Init pager block and item collection with page size and current page number.
     *
     * @return $this
     */
    protected function _prepareLayout()
    {
        $this->itemsPerPage = $this->_scopeConfig->getValue('sales/orders/items_per_page');

        $this->itemCollection = $this->itemCollectionFactory->create();
        $this->itemCollection->setOrderFilter($this->getOrder());
        $this->itemCollection->filterByParent(null);

        /** @var \Magento\Theme\Block\Html\Pager $pagerBlock */
        $pagerBlock = $this->getChildBlock('sales_order_item_pager');
        if ($pagerBlock) {
            $pagerBlock->setLimit($this->itemsPerPage);
            //here pager updates collection parameters
            $pagerBlock->setCollection($this->itemCollection);
            $pagerBlock->setAvailableLimit([$this->itemsPerPage]);
            $pagerBlock->setShowAmounts($this->isPagerDisplayed());
        }

        return parent::_prepareLayout();
    }