When you “install” an app using HPM, it just puts the code on your hub. You still have to go to apps (or in this case, Integrations) tab and click the “add user Integration” button and choose the app to install. That will put it in your list of installed apps.
Once installed, you’ll need to open it and enter your credentials and a device should get automatically created for the thermostat.
Here is the thread for HPM if you have any problems specific to it: [RELEASE] Hubitat Package Manager (HPM) -- HubitatCommunity