There are a couple code changes from the main UNTZtrument guide, but for the most part the code is the same as the USB MIDI examples in that guide. The biggest change is the addition of the Adafruit BluefruitLE nRF51 Library, which you should have installed while following along with the Feather Bluefruit M0 or 32u4 setup guides.
Here is the full list of Arduino Libraries you will need to install using the Arduino Library Manager.
Two BLE examples exist in the UNTZtrument library:
Navigate to the Adafruit UNTZtrument examples in the File→Examples menu of the Arduino IDE and select one of the BLE examples. Follow the standard upload procedure to upload the example sketch to your Feather M0 or 32u4 Bluefruit LE.
If you need more help with the upload process, visit the 32u4 Bluefruit LE Feather Guide or the M0 Bluefruit LE Feather Guide for more information about using the Feather Bluefruit LE with the Arduino IDE.
Now that we have an example loaded on the Feather, we can connect to a BLE MIDI compatible device.