by Nidhi Tiwari.
Hi Nishant,
I found the solution.
Add below code in /enrol/manual/ajax.php before echo json_encode($outcome);
require_once($CFG->libdir.'/moodlelib.php');
$body = "You have been enrolled to course"."".$course->fullname."<br/><br/>"."Please login to start your course."."<br/><br/>"."Thanks,"."<br/>Admin";
email_to_user($user,$USER,'Enrollment Notification','The text of the message',$body);