How to override a node in an xml file of a ui_component

I have this xml file in some third party module having this content

<?xml version="1.0" encoding="UTF-8"?> <form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd"> <fieldset name="actions"> <field name="simple_action"> <argument name="data" xsi:type="array"> <item name="config" xsi:type="array"> <item name="sortOrder" xsi:type="number">10</item> <item name="template" xsi:type="string">Mexbs_ApBase/form/element/simple-action</item> </item> </argument> </field> <container name="action_details"> <argument name="data" xsi:type="array"> <item name="config" xsi:type="array"> <item name="sortOrder" xsi:type="number">20</item> </item> </argument> <htmlContent name="html_content"> <argument name="block" xsi:type="object">Mexbs\ApBase\Block\Adminhtml\Promo\Quote\Action\Details\Staging</argument> </htmlContent> </container> ... ... </fieldset> </form> 

and then I want to change this block URL inside the below htmlContent node

 <htmlContent name="html_content"> <argument name="block" xsi:type="object">Mexbs\ApBase\Block\Adminhtml\Promo\Quote\Action\Details\Staging</argument> </htmlContent> 

to "Mexbs\ApBase\Block\Adminhtml\Promo\Quote\Action\Details"

I have already created a module to override the file, and tried to do so by rewritting the whole file in my own module with the intended changes made and it worked, but I want to only include this node needed to be changed in my file not the whole file.

How can I do so? Thanks in advance