When you download the file, make sure the filename (excluding the extension) exactly matches your video file's name, or rename them both to match, so your media player (like VLC) loads the subtitles automatically.
You can typically find these subtitle files (usually in .srt format) on community-driven subtitle repositories or fansub forums. Since these are often hosted on niche sites, here are the best places to look for this specific version: subtitle REMINISCENCE.2021.SUBFRENCH.FANSUB.WEB...
This appears to be a release title for a French fansub of the 2021 film , starring Hugh Jackman. When you download the file, make sure the