Your Sina elliptical has been fitted with a built-in wireless heart rate receiver that's compatible with uncoded, 5Khz frequency transmitters. An example of a compatible transmitter is the Polar T31 uncoded transmitter.
To get a heart rate reading using a chest belt, put the chest belt on, positioning it in the middle of your chest just above the solar plexus. There is no need to pair the transmitter to the receiver.
Get on the Sina, power it up and begin your workout. The chest belt will automatically send out a signal that the wireless receiver will pick up. Your heart rate will be displayed on the screen.