First, obtain Harry potter movies somehow or other. And then, search the appropriate subtitles at Subscene https://subscene.com/subtitles/title?q=harry+potter&l=

Do you use torrent? Search 토렌트 at Google. And access anywhere which is written in Korean. And Search Harry potter or 해리포터. Or if you have the movie file, just search 해리포터 한글자막 at Google.