Hi,
For the apply for course button or any course button you can link it to the external link refer this tutorial:
https://vibethemes.com/documentation/wplms/knowledge-base/connect-take-this-course-button-to-external-page-2/
For the register page add the below code in your wplms-customizer.php file present in your wplms customizer plugin.
add_action('template_redirect',function(){
global $post;
$register_page_id = $id = vibe_get_bp_page_id('register');
if( $post->ID == $register_page_id ){
$page = 'http://vibethemes.com';
wp_redirect($page);
exit;
}
},1);
NOTE:
=> In the above code please change the http://vibethemes.com to your external link.
=> Make sure the buddypress register page is connected in wp-admin->settings->buddypress->pages->register.
Now this page will not open, and everytime any user tries to open this page the user will be redirected to the page set in the code.