https://wordpress.org/support/topic/remove-footer-powered-by-wordpress-theme-catch-kathmanu

First, create a child theme and then in your functions.php, create a new catchkathmandu_footer_content()function like this:

<?php    function catchkathmandu_footer_content() {      echo "I like pie.";  }    ?>

Obviously, replace the pie line with whatever you'd like to display in the footer.

As per the instructions in catchkathmandu-functions.php just add this to your functions.php in a child theme:

function catchkathmandu_footer_content() {  	}

You can put whatever code you want in there. So I put:

function catchkathmandu_footer_content() {  	echo 'Copyright MYSITE. All rights Reserved. <a href="MYEMAIL">Contact</a>';  }