How to Add Placeholder Text to Fields in Checkout in Magento 2

1) First of all, Let’s assume that you have created a simple module. After that, You need to create di.xml to create plugin at app/code/Module/Helloworld/etc/frontend/ and paste the below code :

<?xml version="1.0" ?>
<!--
/**
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Checkout\Block\Checkout\AttributeMerger">
        <plugin name="add_placeholder_to_checkout"
            type="Module\Helloworld\Plugin\Block\Checkout\AttributeMerger"
            sortOrder="10"/>
    </type>
</config>
2) Then, You need to create AttributeMerger.php file at app/code/Module/Helloworld/Plugin/Block/Checkout/ to add placeholder code and paste the below code :
<?php  namespace 
Module\Helloworld\Plugin\Block\Checkout\; 
/**  * Class AttributeMerger  * @package Module\Helloworld\Plugin\Block\Checkout\AttributeMerger 
 */ class AttributeMerger 
{     /**      * @param \Magento\Checkout\Block\Checkout\AttributeMerger $subject      * @param $result      * @return mixed      */    
 public function afterMerge(         \Magento\Checkout\Block\Checkout\AttributeMerger $subject,         $result     ) 
    {         $result['firstname']['placeholder'] = __('Enter First Name');         $result['lastname']['placeholder'] = __('Enter Last Name');     
$result['street']['children'][0]['placeholder'] = __('Line no 1');         $result['street']['children'][1]['placeholder'] = __('Line no 2');         $result['city']['placeholder'] = __('Enter City');      
$result['postcode']['placeholder'] = __('Enter Zip/Postal Code');         $result['telephone']['placeholder'] = __('Enter Phone Number');     
return $result;  
 } }
Now, Just clean cache and check it on your checkout page