how to enqueque code in a php file from functions.php

If that is the sum of the code for that file then the only place near the bottom is that do_action— do_action( 'shiroi_after_post_body_content' );— which looks to be what you want.

function test_new_action() {
  echo 'Howdy';
}
add_action('shiroi_after_post_body_content','test_new_action');

Depending upon how this file is included there might be other hooks.

You can’t add code to the file otherwise without editing it manually or with PHP

For reference (maybe helpful): https://wordpress.stackexchange.com/a/97599/21376