Editing Category Pages

First, be sure to set up a child theme - don't edit the current theme unless it's a completely custom one. Otherwise, whenever you update your theme, your changes will be lost.

To do:

• Check what folder your current theme is in. As an example, say you're using Twenty Nineteen - it's in a twentynineteen folder.

• Create your own folder inside /wp-content/themes/. Perhaps /wp-content/themes/mychild/.

• Create a style.css file inside that folder. It just needs two short comments:

/* Theme Name: My Child Theme Template: twentynineteen */

Note, you need to change the template (twentynineteen) to whatever your actual parent theme's folder is. That's it, you have a child theme. Go ahead and activate it, though it won't actually change anything yet.

• Now create a functions.php file inside that same folder. Here, you're creating your own version of the function, and giving it a higher priority than the 4 that's used in your parent theme, so that yours will win out:

<?php
/*Add noindex to low value pages*/
function add_noindex_tags(){
    # Get page number for paginated archives.
    $paged = intval( get_query_var( 'paged' ) );

    # Add noindex tag to all archive, search and 404 pages.
    if( is_search() || is_404() )
    echo '<meta name="robots" content="noindex,follow">';

    # Add noindex tag to homepage paginated pages.  
    if(( is_home() || is_front_page() ) && $paged >= 2 )
    echo '<meta name="robots" content="noindex,follow">';
}
add_action('wp_head','add_noindex_tags', 5 );
?>

So, the two differences in your child theme's functions.php file are that you have removed is_archive() || from one condition (so the noindex tag will no longer be added to all archives, which includes your categories), and changed the priority on add_action() to 5.