How to override a template file in module creation in Magento2
you can try with below code in xml file,
<?xml version="1.0"?>
<page layout="1column" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceContainer name="content">
<referenceBlock name="product.info.addtocart">
<action method="setTemplate">
<argument name="template" xsi:type="string">Hello_Custom::product/view/addtocart.phtml</argument>
</action>
</referenceBlock>
</referenceContainer>
</body>
</page>
There are three methods available to override template files in Magento
For example: Here we override addtocart.phtml file for simple product.
Method 1:
<referenceContainer name="content">
<referenceBlock name="product.info.addtocart">
<action method="setTemplate">
<argument name="template" xsi:type="string">Vendor_Module::product/view/addtocart.phtml</argument>
</action>
</referenceBlock>
</referenceContainer>
Method 2:
<referenceContainer name="content">
<referenceBlock name="product.info.addtocart" template="Vendor_Module::product/view/addtocart.phtml"/>
</referenceContainer>
Method 3:
<referenceContainer name="product.info.form.content">
<block class="Magento\Catalog\Block\Product\View" name="product.info.addtocart" as="addtocart" template="Vendor_Module::product/view/addtocart.phtml"/>
</referenceContainer>