Put your device in bootloader mode

1. Hold the user button on your device
2. While holding, press and release the reset button
3. Release the user button
4. The device should re-enumerate as a USB serial device named MCUBOOT (or similar)

Bootloader requirement: your MCUboot must be built with serial recovery enabled. Required Kconfig in sysbuild/mcuboot.conf: CONFIG_MCUBOOT_SERIAL=y and CONFIG_BOOT_SERIAL_CDC_ACM=y, plus a mcuboot-button0 DT alias for the trigger button. See tikk-fleet's config as a reference. Without this, your device will not respond to firmware upload requests.

When you click Continue, you'll be prompted to pick the bootloader's serial port.