If you have a digital copy or a ripped version of the film where the subtitles are missing or out of sync, third-party repositories like OpenSubtitles or Subscene are the industry standard. When downloading, look for files labeled:
If you are watching La La Land on a streaming service: la la land subtitles english
If you download a subtitle file but the text appears too early or too late, you don't need to download a new file. You can adjust it in your media player. If you have a digital copy or a
In VLC Media Player:
In MPC-HC / Media Player Classic:
The 4K Ultra HD and Blu-ray releases of La La Land contain the definitive English SDH track. These are QC'd (Quality Controlled) by the studio. The Blu-ray even includes a "Lyrics subtitle" track that only displays song lyrics. In MPC-HC / Media Player Classic: