Removing and editing content blocks

I’m kinda new to WordPress so maybe I’m doing something wrong.

I have inherited a website built by somebody else and am editing it. I have noticed that you can remove blocks from the homepage by physically deleting them from the index.php file within wp-content (I have direct access to the files on the web server).

However, this does not remove them from “mywebsiteurl/wp-admin”? Is there a way to delete blocks from “mywebsiteurl/wp-admin”? Because now it says I have blocks in wp-admin Pages that are not in index.php anymore!

==Second Question==

I want to add a few headers below some previously made text, in a previously made div. Here is the original code in index.php:

<div class="two pad-right">
<?php while (have_posts() ) : the_post(); ?>
    <h1>?php the_field('main_header'); ?></h1>
    <div>
        <?php the_field('intro_text'); ?>
    </div>
</div>

I tried doing something like this:

<div class="two pad-right">
<?php while (have_posts() ) : the_post(); ?>
    <h1>?php the_field('main_header'); ?></h1>
    <div>
        <?php the_field('intro_text'); ?>
        <h2><?php the _field('intro_text_extra');?></h2>
    </div>
</div>

But “Intro Text Extra” does not appear in mywebsiteurl/wp-admin” Pages and then Homepage? “Main Header” and “Intro Text” are there but not “Intro Text Extra”.