First of all make sure your curtain is configured properly in Thinka (see KNX) as a window covering. Now just say: "Hey Siri, close the blinds". You can also open the blinds partly. Then you can just say: “Hey Siri, set the curtain to 30 percent”. Note that 100% is fully open (most light).
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