Each On Premise Agent is installed as a Service on a Windows host of your choosing. A host can have multiple agents installed, as you noted.
You can install another agent on a different host by logging into Scribe Online from that host and adding another On Premise agent. Select the (+) icon in the top right of the Agent screen. Select this Agent in an existing or new solution. Be sure to test any Connections you'll be using with this Agent.
Please note that once an agent is installed, it is tied to your Scribe Organization and the host it was installed on. It cannot be moved.