How to Override Block in Magento 2

Configure Module

Create module.xml at app/code/Magemonkeys/RewriteContact/etc and add the following code inside it:

<?php
MagentoFrameworkComponentComponentRegistrar::register(
MagentoFrameworkComponentComponentRegistrar::MODULE,
'Magemonkeys_RewriteContact',
__DIR__
);

Override di.xml File

Now, I will override di.xml file. Create di.xml at app/code/Magemonkeys/RewriteContact/etc and add following code in the dl.xml file.

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<preference for="MagentoContactBlockContactForm" type="MagemonkeysRewriteContactBlockContactForm" />
</config>

Override Contact Form

It’s time to override contact form. Create ContactForm.php at app/code/Magemonkeys/RewriteContact/Block and add following code in this newly created file:

<?php
namespace MagemonkeysRewriteContactBlock;
use MagentoFrameworkViewElementTemplate;
class ContactForm extends MagentoContactBlockContactForm{

public function getText() 
{ 
return "Override Contact Block"; 
}
}

Override contact_index_index.xml

Create contact_index_index.xml at app/code/Magemonkeys/RewriteContact/view/frontend/layout and add following code in this file:

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">    
   <body>     
      <referenceBlock name="contactForm" remove="true"/>   
       <referenceContainer name="content">
           <block class="MagentoContactBlockContactForm" name="customContactForm" template="Magemonkeys_RewriteContact::form.phtml" />
       </referenceContainer>
   </body>
</page>

Override form.phtml

Go to vendor/magento/module-contact/view/frontend/templates from the root directory of your store and copy the form.phtml file to app/code/Magemonkeys/RewriteContact/view/frontend/templates folder.

Now, you just need to update the form.phtml by adding following code:

<?php
/**
* Copyright © 2013-2017 Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
// @codingStandardsIgnoreFile
?>

<form class="form contact"

     action="<?php /* @escapeNotVerified */ echo $block->getFormAction(); ?>"

     id="contact-form"

     method="post"

     data-hasrequired="<?php /* @escapeNotVerified */ echo __('* Required Fields') ?>"

     data-mage-init='{"validation":{}}'>

   <fieldset class="fieldset">
       <legend class="legend"><span><?php /* @escapeNotVerified */ echo __('Write Us') ?></span></legend><br />
       <div class="field note no-label"><?php /* @escapeNotVerified */ echo __('Jot us a note and we’ll get back to you as quickly as possible.') ?></div>
<div class="field note no-label"><?php echo $block->getText(); ?></div>
       <div class="field name required">
           <label class="label" for="name"><span><?php /* @escapeNotVerified */ echo __('Name') ?></span></label>
           <div class="control">
               <input name="name" id="name" title="<?php /* @escapeNotVerified */ echo __('Name') ?>" value="<?php echo $block->escapeHtml($this->helper('MagentoContactHelperData')->getPostValue('name') ?: $this->helper('MagentoContactHelperData')->getUserName()) ?>" class="input-text" type="text" data-validate="{required:true}"/>
           </div>
       </div>
       <div class="field email required">
           <label class="label" for="email"><span><?php /* @escapeNotVerified */ echo __('Email') ?></span></label>
           <div class="control">
               <input name="email" id="email" title="<?php /* @escapeNotVerified */ echo __('Email') ?>" value="<?php echo $block->escapeHtml($this->helper('MagentoContactHelperData')->getPostValue('email') ?: $this->helper('MagentoContactHelperData')->getUserEmail()) ?>" class="input-text" type="email" data-validate="{required:true, 'validate-email':true}"/>
           </div>
       </div>
       <div class="field telephone">
           <label class="label" for="telephone"><span><?php /* @escapeNotVerified */ echo __('Phone Number') ?></span></label>
           <div class="control">
               <input name="telephone" id="telephone" title="<?php /* @escapeNotVerified */ echo __('Phone Number') ?>" value="<?php echo $block->escapeHtml($this->helper('MagentoContactHelperData')->getPostValue('telephone')) ?>" class="input-text" type="text" />
           </div>
       </div>
       <div class="field comment required">
           <label class="label" for="comment"><span><?php /* @escapeNotVerified */ echo __('What’s on your mind?') ?></span></label>
           <div class="control">
               <textarea name="comment" id="comment" title="<?php /* @escapeNotVerified */ echo __('What’s on your mind?') ?>" class="input-text" cols="5" rows="3" data-validate="{required:true}"><?php echo $block->escapeHtml($this->helper('MagentoContactHelperData')->getPostValue('comment')) ?></textarea>
           </div>
       </div>
       <?php echo $block->getChildHtml('form.additional.info'); ?>
   </fieldset>
   <div class="actions-toolbar">
       <div class="primary">
           <input type="hidden" name="hideit" id="hideit" value="" />
           <button type="submit" title="<?php /* @escapeNotVerified */ echo __('Submit') ?>" class="action submit primary">
               <span><?php /* @escapeNotVerified */ echo __('Submit') ?></span>
           </button>
       </div>
   </div>
</form>

I have added <?php echo $block->getText(); ?> under <div class=“field note no-label”> in order to display it in a clear and decent format.

Run Commands

Go to the root directory of your store and run the following commands:

php bin/magento module:enable Magemonkeys_RewriteContact
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy
php bin/magento cache:clean
php bin/magento cache:flush