Tags doesn't work

Hi people,

I’ve just published a new blog called https://www.boombamblog.dk,
but there’s a problem with the tags in the posts. If you click the tag i get this error:

Fatal error: Call to undefined function single_tag_() in /customers/2/e/d/boombamblog.dk/httpd.www/wp-content/themes/autofocus/archive.php on line 35

Line 35 in archive.php says:

<?php printf( __( ‘Tag Archives: %s’, ‘autofocus’ ), ‘<span>’ . single_tag_( ”, false ) . ‘</span>’ ); ?>

What do I do to fix this? Any help would be appreciated..

Thanks in advance ??