If you want to save a voice recording as an MP3, your best bet is to use a dedicated MP3 player. Some smartphones and tablets also come with MP3 players pre-installed, but if not, you can usually download one from the app store. Once you have the MP3 player, open the recording and select "Create a New Audio File" from the File menu. You'll then be, prompted to name the file and choose a location to save it.