Subtitles and Audio stream Unkown.



Hello everyone. I am a newbie here and honestly I wanted some help in setting up plex. I have been able to upload my movies successfully and I want some help in setting subtitles for the movies I have downloaded. I have hearing deficit so I would really want subtitles in my movies. I went and checked the forums and tried various ways to add subtitles, I even have external subtitles added to my movies in the proper order with proper file names, then I saw that my audio stream was set to unknown. Is it possible that this is causing an issue with the subtitles. I also have registered to open subtitles. But nothing seems to be working. Can anyone tell me if I can convert or do something with the video file so that it can recognize the audio stream? Any other way to use subtitles other than open-subtitles, I can even use the external ones cause they arent showing up. Thank You.
Concerned new plex user.