Hi @nsilva
I believe you can get the post based on the keyword using the “s” parameter. This page should give you more idea about it: https://codex.wordpress.org/Class_Reference/WP_Query#Search_Parameter. Something like this:
// update meta query
$query->set('s', 'the keyword');
$query->set('meta_query', $meta_query);
Hope this helps.
