Simply go to the 'Plugins' page, search homebridge-thermobit and click 'Install'.

This will only work if you are using a platform which installs plugins globally.

sudo npm i homebridge-thermobit -g

If you use the Homebridge UI or HOOBS then a configuration screen will appear after installing the plugin where you can enter your Thermobit credentials. You can optionally use a base64-encoded version of your password.

See the Configuration page for JSON configuration templates and other optional settings if editing the configuration manually.

And voila your Thermobit devices should be added to your Homebridge/HOOBS instance.