You have to turn the light on and off quite often until it goes into pairing mode. I think the device needs like 6 cycles to reset and goes into pairing mode when you turn it back on again. The light bulb starts to automatically adjust its brightness and/or colors when it’s waiting for pairing. If it’s not, it also isn’t in paring mode AFAIK.
If your bulb is discovered but shows up as “Unknown Device” and is unusable after seemingly successful pairing, it might be related to this issue: Problem with fresh Openhab 2.5 / Zigbee / Bitronvideo Ember Dongle / Device Pairing