Check IP and password (of the server) to connect by SSH.
Connect to server by SSH.
5*. An advice: install remote desktop on linux and configure remote access to desktop (Ubuntu desktop and x2GO for Ubuntu for example).
Update the system.
Create new user in system.
Reboot the system.
Connect to server by SSH (or remote desktop) as a new user.
Install Project Zomboid dedicated server by steamCMD.
Full guide will be soon!
Here shortly -