Copy the footer.php page from the Twenty Fifteen theme to the Twenty Fifteen child theme folder
<?php
/**
* The template for displaying the footer
*
* Contains the closing of the “site-content” div and all content after.
*
* @package WordPress
* @subpackage Twenty_Fifteen
* @since Twenty Fifteen 1.0
*/
?>
</div><!– .site-content –>
<footer id=”colophon” class=”site-footer” role=”contentinfo”>
<div class=”site-info”>
<?php
/**
* Fires before the Twenty Fifteen footer text for footer customization.
*
* @since Twenty Fifteen 1.0
*/
do_action( ‘twentyfifteen_credits’ );
?>
<a href=”<?php echo esc_url( __( ‘http://example.com/’, ‘twentyfifteen’ ) ); ?>”><?php printf( __( ‘© 2015 %s’, date( “Y” ), ‘twentyfifteen’ ), ‘Example’ ); ?></a>
</div><!– .site-info –>
</footer><!– .site-footer –>
</div><!– .site –>
<?php wp_footer(); ?>
</body>
</html>