In Hongdae, try Olive Young Hongdae Town (57 Hongik-ro 6-gil) or Hongik Univ.

Station Store (156 Yanghwa-ro), both 10:00-23:00, half an hour later than many stores. For concealer, the Skin Fit Cover Liquid Concealer has 4,676 reviews, 화이트컨실러 means there's a white shade for brightening, and 무펄하이라이터 = a no-glitter highlighter, so photos don't look greasy.