It will likely be a .srt , .ass , or .sub file. .srt is the most universal.
Open the movie in VLC Media Player (recommended). Go to Subtitle -> Add Subtitle File and choose your downloaded .srt . gloomy sunday english subtitle download link
This is critical. If your movie file is named Gloomy.Sunday.1999.mkv , rename the subtitle file to exactly Gloomy.Sunday.1999.srt . It will likely be a