In WordPress, customizing your own 404 page is done by changing the theme template.
To change your 404 page, do the following:
<?php get_search_form(); ?>
<?php _e('text'); ?>
The default template for the Twenty Nineteen theme looks like this:
<?php get_header(); ?> <section id="primary" class="content-area"> <main id="main" class="site-main"> <div class="error-404 not-found"> <header class="page-header"> <h1 class="page-title"><?php _e( 'Oops! That page can’t be found.', 'twentynineteen'); ?></h1> </header><!-- .page-header --> <div class="page-content"> <p> <?php _e( 'It looks like nothing was found at this location. Maybe try a search?', 'twentynineteen' ); ?> </p> <?php get_search_form(); ?> </div><!-- .page-content --> </div><!-- .error-404 --> </main><!-- #main --> </section><!-- #primary --> <?php get_footer();