This tutorial will show you how to convert m4a audio files to mp3 format on macOs with iTunes.
Step 1 – Launch iTunes, goto top menu iTunes -> Preferences, General tab, click the button Import Settings, change the option Import Using to MP3 Encoder.
Step 2 – In iTunes, select Music, find your song in the Music Playlists.
If your m4a audio is not listed there, right click on the m4a file, select Play With -> iTunes and play it with iTunes.
Step 3 – Select the song, then goto iTunes top menu File -> Convert -> Create MP3 Version.
Step 4 – After the conversion is finished, drag the newly created file and drop it on desktop.