The Course Add & Drop period for Fall 2023 will start from 

September 5 (Wed.), 10:00 until September 7 (Thu.), 17:00 KST.

During this period, you can register for courses with available seats the same way you did during the Course Registration Period in August (first-come-first-serve).

but unlike the regular period, there won't be any major-related restrictions for selecting courses, so you are free to choose courses with available seats.

Changing (or removing) courses WILL NOT be possible after this period, under any circumstance, so be sure to make the changes during this time.