Booting from linux usb

Hi, I have a Lenovo Flex3 Chromebook which I recently powerwashed, but I am stuck at the network section of the setup because the Chromebook is not picking up any Wifi networks. I am therefore stuck right at the start of the setup and only have access to the developer console.

I would like to boot Ubuntu from a bootable USB but whenever I select “Boot from external disk” or “Select alternative bootloader”, the laptop makes a loud beep and I get the message “No valid image detected”.

I have searched on the internet and tried the recommended command

crossystem dev_boot_usb=1

to no success. Some people have said maybe the firmware for this laptop is outdated and needs to be updated from, however I don’t have internet to perform the curl commands in the terminal to obtain the .sh files.

You could try using wired internet by using a Ethernet to USB-C adapter.