Only one iCloud account can be linked to the Hue bridge using the HomeKit setup code. In order to gain access to the Hue bridge, ask the person who has setup the system to share control of HomeKit accessories. To share HomeKit control, open the Hue app, select Settings > Siri voice control > icon on the top right > Invite People.
Note: Make sure you only share to trusted persons, since this will share control to all your HomeKit accessories, not limited to the Hue lights. If you lost your iCloud credentials, you can only remove pairing by resetting the bridge (warning: all Hue settings including lights, devices alarms &timers will be lost).
For more information, visit: support.apple.com/HT204893