First of all make sure your lamp is configured properly in Thinka (see Lightbulb) as a lightbulb. Then you can just say: “Hey Google, set the floor light to 50 percent” or "Dim the floor light by 20 percent".
In case something is not clear or not working according to your expectation you can contact us, and we will provide instant feedback. We can be reached by email at support@thinka.eu, or by phone at +31-20-2420666