Regarding immigration issues like Alien registration or Visa extension, you can make On-line reservation before visiting the Immigration office.

Please refer to the attachment [Hi Korea On-line Reservation Guide]. You can find the information about how to make on-line reservation. It would be helpful to save your time.

Website  for online reservation: http://www.hikorea.go.kr

Video Link : https://www.youtube.com/watch?v=4fT5oDX0_yw