Go to cli prompt of Rpi

In the latest version of HA (2021.3.4) you can install ssh.
That is working fine in the HA area !

But how can I go to the root of the Host software on the Rpi, because I need to add some extra python scripts on the host Rpi to collect data from an other system.
Also I need to activate the I2C bus to connect an small electronic design on the Rpi.

So in short:
How can I go to the Rpi standaard prompt, not the root of HA but the pi ‘root’

Thanks,
Eric