Record Internal audio with Replay or Peek during screencast

Hello everyone,

I need to re-record videos that are slightly broken. For this reason, I just want to film the videos and record the internal sound of these videos. Unfortunately I can't find a setting and can only record microphones etc., but I only need the internal audio or the existing voice in the videos I want to record. Are there any workarounds? I've found other post but couldn't get it to work.

Thanks very much in advance.

Greetings Paul