According to this Korean article: ????, ???? ??? ?? 12? ??

Seoul Express AREX starts again on May 30. You can buy tickets online from May 12, and even get a TINY discount if you register as a member. HOWEVER, don't be surprised if they don't have an option for foreign registration or foreign cards (this happens so often).

Also, it says that the Seoul Station Check in will "restart next month." No specific date given.

I also went for a check on the Gangnam COEX Check In, and alas - they specifically state it's closed until Sept 30, 2022. Yes, the original post is old - but Korea will often update the same post with the new information, so I trust it. There's literally nothing else. https://www.calt.co.kr/custom/custom...ce&cat_check=C

No updates about Gwangmyeong check-in.