The fw update procedure is not tidied up yet so we have to resort to this:

preparation:
- disconnect power from gliss
- remove Gliss from the rack and get a jumper or a screwdriver or another metallic object to short two pins together in the update procedure
- get a USB micro cable that you can connect to the computer
- make sure you have Google Chrome installed
- power off Gliss by disconnecting the USB cable from the computer
- download the firmware: https://files.bela.io/22c117ade5-d78d5eef6a-9c902046c3-20b6fc4801-G491KE-TrillRack.bin

update procedure
- use Google Chrome
- short the BOOT and 3V3 pins at the back of Gliss with a jumper or screwdriver. Keep them shorted while you power up Gliss. After it's powered up, remove the short.
- open this page https://devanlai.github.io/webdfu/dfu-util/
- click Connect. In the dialog that shows up select "DFU in FS mode" and click Connect again
- in the following dialog "our device has multiple DFU interfaces. Select one from the list below:", select the first one, which contains "Internal Flash" and click "select interface"
- go to "firmware download" and press the "Choose file" button
- select the file *G491KE-TrillRack.bin that you downloaded above
- press "Download" . You'll see progress bars for "Erasing DFU device memory" and "Copying data from browser to DFU device".
- You'll get 
Wrote 271016 bytes
Manifesting new firmware
DFU GETSTATUS failed: stall
Done!
- that means success (despite the failed: stall message)
- power off gliss, remove the short between 3v3 and BOOT if it's still there)
- power on Gliss, it should have the new firmware. It should be blinking red and yellow to take you through factory test mode. You can skip that: [ress the button and two fingers to enter the menu, tap the green selector. Now you are in control mode. Make sure you run through calibration if you need accurate I/O voltages.