The ideal way would be to add the iframe in the unit itself however, since you want to apply to all units following code will help.
add_filter('bp_course_api_get_user_course_status_item_unit_meta',function($meta){
if(empty($meta['iframes'])){$meta['iframes']=[];}
$meta['iframes'][] = 'https://ig1kqagxzl.preview.infomaniak.website/wp-content/uploads/acordium/index.html?tipo?diatonico&sibtip=DGC&fixed=1';
return $meta;
});
the above code will add your iframe video in all the units of your course.