First check the date and venue, advance reservation, whether foreign phone numbers are accepted, and on-site waiting. Reading both this site's event post and the organizer's original notice can save you a wasted trip.
Checking the schedule
Check this year's announcement and the end date
Checking entry
Distinguish reservation-only, on-site waitlist, and free entry
CatchTable Global describes a reservation and waitlist service for foreign travelers. If you don't have a Korean number, look for participating restaurants in the Global app.
Service to use
CATCHTABLE Global
Things to distinguish
Confirmed reservation / on-site or remote waitlist