Here is a simple how to instruction to enable the Fan and Power on / off functionality on the ArgonOne Case.
DarkElvenAngel made a really nice Argon One Daemon
that can be found on DarkElvenAngel / Argon One Daemon · GitLab
On a fresh install of OSMC you need to do the following:
sudo apt-get update
sudo apt-get install i2c-tools libi2c-dev
sudo nano /etc/modules
In modules I added i2c-dev
sudo nano /boot/config-user.txt
In config-user.txt I added dtparam=i2c1=on
reboot
sudo apt-get install gcc device-tree-compiler git bash make libc6-dev
git clone https://gitlab.com/DarkElvenAngel/argononed.git
cd argononed/
./configure
./install
reboot
You can test the fan by typing argonone-cli --manual --fan=100 and set it back to auto using argonone-cli --auto