In K-pop, "couple" refers to shipping two idols. 19 could be the age or a suggestive concept. s2 = season 2 of a fanfiction series. indo = Indonesian fan translation. eolgongchuga = possibly a misspelling of eolgul bit chuga (얼굴 빛 추가) – "face light addition" – or a coined ship name.
Based on the structure, the phrase appears to be a mix of: s2couple19 eolgongchuga indo18 new
This is the most distinctive part. It does not appear in standard Korean dictionaries. Breaking it down: In K-pop, "couple" refers to shipping two idols