Adding another bulb to your hub is very easy!
Simply press the discovery button on your hub and turn on your light. If your light is at factory settings, it should join automatically within seconds.
For the Nanoleaf Ivy, the light will pulse gently when searching for a Hub and will pulse strongly when it joins the hub. For other ZigBee lights, please refer to manufacturer information to understand any visual cues.
Once the light has joined, you should be able to control it in your iOS App, assuming you have added the hub to HomeKit.
For reset procedures of other manufacturers: