Air Busan, Eastar Jet, Jeju Air, Jin Air, T'way Airlines.
There are border closure exemptions for holders of a valid Korean visa, including the 'K-ETA' for eligible travelers. Exemptions are revoked if another country has been visited in the previous 14 days that is considered high risk. More information on exemptions and high-risk countries can be found at https://www.koreanair.com/at/en/travel-update/covid19/travel-restriction/korea
Travelers must be quarantined for 10 days upon arrival at a government-run quarantine facility, at the traveler's expense. Nationals and long-term residents can complete the quarantine period at their private residence.
Proof of a negative COVID-19 test, taken within the previous 72 hours, to be provided upon departure. This document must be printed and written in Korean or English. Accepted tests include NAAT, PCR, LAMP, TMA, SDA, and NEAR
For more details HERE