The compressed audio should be in a WAV-file. Open the file with XMPlay, then set the Output device to 'WAV Writer' (see here
). Play the file, and XMPlay will ask you where to save the new WAV-file with decompressed audio.
Note that XMPlay is not designed to do these conversions, but it can do it. There are dedicated programs if you need to do this regularly, like dBpoweramp
and many other converters.