Example of how to filter the 'Nothing in your Event Queue' additional details text.

example.php

<?php //Please do not include the opening PHP tag if you already have one 

function tw_ee_filter_emtpy_queue_desc_text() {
  $new_text = sprintf(
      __('You need to %1$sReturn to Events list%2$sselect at least one event%3$s before you can proceed with the registration process.',
      'event_espresso'),
      '<a href="' . get_post_type_archive_link('espresso_events') . '" title="',
      '">',
      '</a>'
  );
  return $new_text;
}
add_filter( 'FHEE__Single_Page_Checkout__display_spco_reg_form__empty_msg', 'tw_ee_filter_emtpy_queue_desc_text' );