You have to use a video editor software. Like adobe premiere pro. Sony vegas pro.....

Download the subtitle file..mostly it have '.srt' extension......and the subtitle menu location depends on the media player you are using...find and click on that...then click on add subtitle and select your subtitle file

@subtitle_dl_bot Try to find the subtitle using this bot, or download the subtitle and then open the video with vlc. Right click- subtitle - add subtitle file

I meant to say .srt

First download the subtitle file usually .sry and just drag and drop it on the video file you opened in the player....this is for potplayer but it might work on others