Step 1 - Plug in your device

Use a USB-C cable. If your TRMNL includes this accessory, that works too.

Step 2 - Enter "flashing mode"

First, turn off the device. Then, while pressing down on the circular button below the power switch, turn the device back on. Let go of the circular button.

Step 3 - Flash firmware

Click 'Connect' below, then select your device from the list. Its name will start with "USB JTAG/serial."