Change searched term

The pre_get_posts filter is the right place to go. You can check if you are on a search query, and alter it the way you want. Here’s an example:

function search_filter($query) {
  if ( !is_admin() && $query->is_main_query() ) {

    // Check if we are on a search page
    if ($query->is_search) {

      // Get the search query
      $search_term = get_search_query();

      // You can modify the search query here, and pass it to the query again.
      $search_term = str_replace( "-", "" , $search_term );

      $query->set( 's', $search_term  );

    }

  }

}

add_action('pre_get_posts','search_filter');