I have recorded 7 you tube videos on my samsung 1 SV, however the sound was a poor quality. I wish now to record over the 7 Yiu tube videos using audacity. Please help 
Thanks Sheila
Do you know why the original track was damaged?
We’re not a video editor and even if we do help you with your project, all we can do is create a terrific sound track. We can’t jam it back into the video.
Connect your high quality microphone in a nice echo-free, quiet room, start Audacity, and then start the movie on the other computer or movie player. Use the real movie (with the volume turned down) as a guide to where the new dialog has to be. When you’re finished speaking, Export your sound track as a WAV, 48000 Hz, 16-bit Stereo (video standard) and use your video editor in sound-only mode to integrate the new track.
You may need to time shift or make other changes so the new track fits, but that’s basically it.
If you have to stop and start because of speaking mistakes, then the process is going to be really time consuming and error prone.
If you have a nice video editor you may be able to convince that to do the new track capture and short cut all those tasks and tools – not use Audacity at all.
Koz