first time one connects a bluetooth device the device needs to be put into pairing/ discovery mode
to show up,
how you go about placing the bluetooth device in question into pairing mode differ from device to device it should be in the documentation of the device or on the manufactures website.
you can also google
<name of bluetooth device and model number> pairing mode and get some hits
plus if a bluetooth have an active connection with another device at the time pairing will in most cases not work, at times I've had to disable bluetooth on my iphone or devices liked to auto connect to it