editing iphone memo recordings

I want to edit a recording I made with my iPhone memo function. This generates .m4a files, but these are not recognized by Audacity as m4a files. Is there some conversion I need to do? Any suggestions how to accomplish the needed editing?

Have you tried using Audacity 1.3.12 with FFMpeg installed?

Alternatively, you could convert the file to WAV format with a suitable file converter program, then import and edit the WAV file.

If you have free iTunes, you can use that to convert files into plain WAV.

iTunes (or Edit) > Preferences > General > Import Settings > WAV Encoder.
Open the work in iTunes and Advanced > Make WAV Version.