You could use Node-Red.... if you have basic knowledge of JavaScript.

• What API is open to communicate with Google Assistant
• How could I connect to device from the API

If you do not know the API, your start there and do the basic things.

If you do not know the protocol to use to communicate you need to solve that

Siemens Logo could listen for events from event-driven approach like Node-Red to get analog signal to be your input for your ComfortSoft program. (your logic)

You could start here

https://googlehome.hardill.me.uk/

Its a bridge between your google cloud account and Node-Red. You could think Node-Red as Gateway to speak different protocols. The great thing about it you do not have to know 'How it works' you only need to understand the workflow. That simply the approach in your project to make everything works.