Use an online audio 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 Audacity
Open Audacity
Import the M4A file
Go to File
Select Export
Choose Export as MP3
Save the file
Use iTunes or Apple Music on a computer
Import the M4A file
Export or convert it to MP3 if supported
Save the MP3 file
Use a command-line tool
Install FFmpeg
Run a command to convert M4A to MP3
Save the output as an MP3 file