The way I did it, was to comment it out by adding a <!-- (code) --> around the
WP/ appthemes link info in footer.php,
viz a viz -
<!-- <div class="col-md-4 col-ms-12 col-xs-12">
<p><a href="https://www.appthemes.com/themes/classipress/" target="_blank" rel="nofollow">ClassiPress Theme</a> - <?php _e( 'Powered by', APP_TD ); ?> <a href="https://wordpress.org/" target="_blank" rel="nofollow">WordPress</a></p>
</div> -->
That's for Classipress, but should work on your theme too.