And this is probably one of the reasons Roku's support is lacking at best. They don't want to be answering questions about every channel/app on their platform. If you're having a problem with a particular channel/app, you need to get help from that channel's provider or developer.
In general, if you hear someone describing the action while you're watching a video or movie you need to change the audio track. How you do that may vary by channel/app, but start by pressing the * button on your remote and look for an option to change the audio track.
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