Best done with a Raspberry Pi or another Pico you have available.
With a Raspberry Pi you can use OpenOCD to flash the main board over SWD using two GPIO pins, e.g. 23 and 24. The following config should be saved as openocd.cfg.
source [find interface/raspberrypi-native.cfg]
adapter gpio swclk 23
adapter gpio swdio 24
set CHIPNAME rp2040
source [find target/rp2040.cfg]
adapter speed 100
init
targets
reset halt
program picoave.elf verify
reset run
shutdownOpenOCD can then be started by sudo openocd in the same directory. Flashing will only take a few seconds.
| Signal | RPi Pin |
|---|---|
| SWCLK | 23 |
| SWDIO | 24 |
| GND | any GND |