gilead

The only thing that fully worked for me was the following:
In the functions.php file, instead of

function footer_link() {
	//$weburl = $_SERVER["SERVER_NAME"];
	//$weburlcount = strlen($weburl);
	$anchorthemeowner='<a href="https://www.code-2-reduction.fr/codium/" title="code reduction" target="blank">code reduction</a>';
  	$textfooter = __('A nice revamping of Sandbox theme for <a href="https://www.www.remarpro.com">WordPress</a> by ', 'codium' );
  	$content = '<div id="footer"><div class="center"><p>' .$textfooter. $anchorthemeowner.'</p></div><div class="clear"></div></div></div>';
  	echo $content;

leave only

function footer_link() {
  	$content = '<div id="footer"><div class="center"><p>Your text or whatever</p></div><div class="clear"></div></div></div>';
  	echo $content;
}