This guide is already assuming you have some form of Coreboot installed. Whether that be what you compiled yourself, Skulls, or Libreboot, etc.
We will be flashing internally for the purpose of keeping Skulls up to date.
To start, you will need to boot your Linux distribution of choice with a specific parameter. In the case of Grub this parameter is "iomem=relaxed". You can either add this to your /etc/default/grub file and update grub or edit this in while booting temporarily. It is recommended that you do this temporarily so your system doesn't always have access to write on the chip. You will also need the package "flashrom".
You can fetch Skulls by heading over to the Release page on their Github.
Now that we have flashrom, Skulls, and iomem=relaxed set, we can begin to reflash Skulls.
First we want to extract the tarball so we can access everything. This can be done with the following command:
tar xvf skulls-1.1.3.tar.xz (Within the directory where Skulls was downloaded).
Skulls comes with README's to help in the installation process so we will follow that.
Now we want to run the skulls.sh file as root so we will elevate our privs with sudo.
We need to provide the board name (T430), and the path to the image that will be flashed. And dont forget to change directories into the Skulls folder.
sudo ./skulls.sh -b t430 -i t430_coreboot_seabios_free_4931b978d9_top.rom
Enter "y" for yes to flash and wait for Skulls to finish. Make sure this command is not interrupted by things such as power loss because this could brick your system.
After this, reboot and then your installation is complete!