<?php
add_filter( 'kleo_ajax_query_args', function ( $args ) {
  //  load the terms using LIKE search
  $term_ids = get_terms( [
    'name__like' => $_REQUEST['s'],
    'fields'     => 'ids',
    'taxonomy'   => 'post_tag',
    'hide_empty' => true
  ] );

  $args['tax_query'] = [
    'relation' => 'OR',
    [
      'taxonomy' => 'post_tag',
      'field'    => 'id',
      'terms'    => $term_ids
    ]
  ];

  return $args;
} );