Visit the WiKi page of Multi-Control, you can see the related resources.

Click HERE to download the library. Click Sketch -> Include Library -> Add .ZIP Library, then include the download library, including Joystick and MIDIUSB.

Then go to Github page and download the code.

Unzip the download package. Open multi-control-midi.ino. Then select the board type (Leonardo) and port, and upload the code.

Here is the code: