I watched a film, Indignation, a 2016 American drama film starring Logan Lerman.
By minute 25, the subtitles were out of sync (in disarray). I edited it by myself with the help of Subtitle Workshop. For about an hour, I did either ctrl+A then alt+M, or select ctrl+X then select ctrl+V then alt+M, or select then shift+ctrl+end then alt+M, or whatever possible to make the subtitles in sync again. I succeeded.
I am happy I can solve a trivial problem like this. For those who encounter the same problem, here is the download link. It may not be perfect, but I really did my best. Enjoy!