Installing Nefit Easy (Worchester Wave) smart thermostat


I’m trying to install the Nefit Easy smart thermostat.
I found a tutorial online, but the first thing i’m trying is not working.

When i logged in via SSH, i have to put in the following command:

# at the hassio> prompt

# now at the bash-4.4# prompt
# run shell in homeassistant docker containter
**docker exec -it homeassistant /bin/bash**

When i type that in ssh i get the following message:

core-ssh:~# docker exec -it homeassistant /bin/bash
-bash: docker: command not found

What am i doing wrong?