The most common Korean word for “in advance” is 미리 (miri). 「in advance」는 한국어로 미리.
Learn 미리 free — flashcards, audio and review →「미리」 단어장으로 무료로 외우기Words and levels: TOPIK I essentials (National Institute of Korean Language standard curriculum, KOGL Type 1) · examples: Cheesepotato