WordPress Auto Enrol Users on All Courses

I am using the Masterstudy theme, they have an action which fires after registration:

do_action(‘stm_lms_user_registered’, $user_id);

Right now users subscribe to a membership which gives them a quota e.g. 10. They have to then manually go to each course and manually enrol onto each course.

What i want to do is, as soon as a user registers, auto enrol them to all courses that are published – which means itll also show on their dashboard.

How would I do this – is it as simple as get the current $user_id, get the $course_id and then assign them to the user through the database?