Hello, and welcome!
It's been a while since I flashed Libreboot on my Macbook 2,1 (I need to
update it), but if you are getting errors like command not found, you are
probably in the wrong directly when trying to run the flashrom script. Make
sure you've cded into the correct directory and try again. If you don't have
permission, that you need to run the command with sudo to get full
permissions for that command.
If this doesn't help, please post exactly what's happening in your terminal
and someone will surely be able to help you.