Windows: More recent versions will play m4a files. If your PC or Audio Player won’t recognise this newer format, see below for converters.
Apple Mac: You will have no problems playing m4a files in iTunes or any other application as they are native on that OS.
https://www.onlineconverter.com/m4a-to-mp3 (max 200 mb)
Offline (local) computer conversion
Offline conversion will always be faster, using an application such as iTunes or the free converter above.