mkvextract.exe is a command line tool that is part of MKVToolNix. mkvextract v8.3.0 can be downloaded from here.

Syntax is pretty simple:

mkvextract.exe tracks "D:\video.mkv" 1:"D:\track-1.aac"

Where:
D:\vide.mkv - Source file
1 - Track number ID
D:\track-1.aac - Destination file

mkvextract manual can be found here.