I needed a second audio file and created a layer and placed my video file that has the audio I want in that layer. I edited the audio in that layer and now I want to save the result as an audio file.. preferably an MP3 file. How do I select a specific layer and save just that layer as an audio file?
I would think with Photoshop you may be able to save it as a video mp4 file then find a Video splitter program to split out the audio. Or use and Audio program in the first place rather the using a program like photoshop that can do some basic video editing.
As JJMack said, your workflow is like using nail varnish to paint a garden fence. Use a proper audio processing tool like Audition or an editing program like Premiere.