Add a link to bottom of every course page via a filter

function elc_course_content( $content ) {
    if ( is_singular( 'sfwd-courses' ) ) {
        $link = '<a href="https://elearningcomplete.com/">Visit elearningcomplete.com</a>';
        $content .= $link;
        return $content;
    }
}
add_filter( 'the_content', 'elc_course_content' );