Open the Philips Hue app and go to Settings > Siri voice control > Advanced > Homes. On the screen will find the list of homes and which one is set as primary home, which your current bridge is connected to. When you pair your bridge to HomeKit you can select one of the existing Homes or create a new Home. If you want to control both bridges separately, assign them to two different Homes. Please note that you have to specify the name of the Home when you provide a Siri command to any non-primary Home. Example: “Turn on the lights in my Holiday Home”.