This system can only be used if the colony is showing signs of swarming, i.e. there are queen cells with larvae in them. If queen cells are sealed it is too late as this indicates that the colony may have already swarmed. Here's how to do it:
Bait hives are used to attract a swarm, usually with some drawn comb. Here's how to set one up.
The Demaree method of swarm control was invented by American George Demaree in the late 1800s. It has evolved over the years and requires the beekeeper to separate the queen (and flying bees) from most of the brood (and nurse bees) by manipulating the frames and using a queen excluder. The objective is to separate the unsealed brood and eggs from the queen and thus reduce crowding in the hive by rearranging the boxes vertically.
The result is a hive with little congestion and lots of room for the queen to lay. In essence, the colony “believes” it has already swarmed. Download 'how to do it' notes.
Some people also wipe a little lemongrass oil on one of the frames as apparently bees are atracted to the smell.