By the way, this is my mother in law's recipe which I tweaked here and there.
After five minutes, open the lid again and fluff up the rice using 'forks'. Do not use spoon as this breaks the rice.
In India, we usually put chunks of burning charcoal on top of the lid and leave it. Out here this isn’t possible (unless you have an outdoorsy kitchen). So what you can do is preheat your oven and leave the biryani inside at about 180C for 20-30 minutes. Or if you do not have a big oven (like me), you could heat up a frying pan on the stove and leave the briyani on top of it. You have to keep the heat level at the minimum possible. Leave it for about 20-30 minutes.
You could keep the biryani pot directly on heat. I use the frying pan as a buffer so that my biryani doesn't get burnt. Clever ha? :D