Before you move on to the next step, you need to make sure you will be able to enter the ./flash.sh command without using the Reform's keyboard.

You have two options:

Connect an external USB keyboard.

Copy the ./flash.sh command followed by a new line in your text editor, so that you can paste it and run it without the use of a keyboard.

The script needs to be run as root, so make sure that you are using a root shell, or that sudo will not ask you to enter a password.