Hue bulb unresponsive

I have two Philips Hue bulbs connected directly to an Echo Show and Echo Studio, so no Hue bridge. This has worked well for 2 and half years. The other day I lost mains power to the sockets but not the lighting circuits. Since then neither of the Philips Hue bulbs are responsive to Alexa. I have tried repowering the lights and both Echos and this has had no effect. I would like to rediscover the bulbs but every site talks about using the Hue app to do this. Could someone please tell me how I can reset the bulbs to make them discoverable?