Create Wordpress theme how to add in admin panel -> configure (- Menu), your field?

I need to create a field in the settings that would allow to hide the search form may not correctly formulated a question, I attach below a screenshot and code of the form and its conclusions. Could you tell how to correctly display the form and how to implement the hiding of the element, and add its own fields in the settings.
Form code:
<form class="form-inline my-2 my-lg-0" role="search" method="get" id="searchform" action="<?php echo home_url( '/' ) ?>" >
 <label class="screen-reader-text" for="s">Search: </label>
 <input class="form-control mr-sm-2" type="text" placeholder="Type to search" aria-label="Search" value="<?php echo get_search_query() ?>" name="s" id="s" />
 <button class="btn btn-outline-success my-2 my-sm-0" id="searchsubmit" type="submit">Search</button>

Conclusion in header.php:
<?php get_search_form(); ?>
March 23rd 20 at 19:38
2 answers
March 23rd 20 at 19:40
Here there are the names of standard sections and panels
March 23rd 20 at 19:42
Adding fields can be implemented using the ACF plugin

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