<?php

// Add this to functions.php
add_filter( 'wp_footer', function() {
?>
<script>
(function($) {
  $(function() {
    wp.hooks.addFilter( 'facetwp/set_options/availability', function(opts, data) {
        opts.altInput = true;
        opts.altFormat = 'd-m-Y';
        return opts;
    });
  });
})(jQuery);
</script>
<?php
}, 100 );