Use an online converter
Upload the M4A file
Select MP3 as the output format
Start the conversion
Download the MP3 file
Use VLC Media Player
Open VLC
Go to Media
Select Convert/Save
Add the M4A file
Choose Convert
Select MP3 as the profile
Start the conversion
Save the MP3 file
Use iTunes or Apple Music on a computer
Import the M4A file
Open the file conversion settings
Choose MP3 Encoder
Convert the file
Locate the new MP3 file
Use Audacity
Open Audacity
Import the M4A file
Export the audio as MP3
Save the file
Use a desktop audio converter app
Install the converter
Add the M4A file
Choose MP3 output
Convert and save the file
Use a command-line tool like FFmpeg
Install FFmpeg
Run a conversion command from M4A to MP3
Save the converted file