WordPress SQL query to tag all posts containing a specific word on title

Did a little bit of searching around this site and found some links that should help you achieve your goal

1) Search all posts that match a specific title
– Found this nifty code on another thread here
– A use case example of the above function here

2) Updating the “tags” for a specific post is fairly simple with this function:

  wp_set_object_terms($post_id, 'mytagname', 'post_tag', true);

3) When you put everything together, it should look something like this (this code is untested)

    add_filter( 'posts_search', '__search_by_title_only', 500, 2 );

$query = new WP_Query(
    array(
        's'         => 'title_to_search_for'
    )
);

remove_filter( 'posts_search', '__search_by_title_only', 500 );

if ( $query->have_posts() ) :
    while ( $query->have_posts() ) :
     $post_id = get_the_id();
        wp_set_object_terms($post_id, 'tag_to_add', 'post_tag', true);
    endwhile;

    wp_reset_postdata();
endif;

Good luck!