If you cannot see your luminaire in Luminaires tab it might be that the luminaire is in some other network. Please go to Nearby Devices screen where you can see a list of all Casambi enabled luminaires close to you.
Below you can see a picture that has three luminaires all with different modes:
Unpaired: Luminaire needs to be paired before it can be used
@My Network: Luminaire is in a known network and can be controlled from Luminaires tab when controlling My Network. Go to More -> Change Network and select "My Network" from the list to see the luminaire in Luminaires tab.
Paired: Luminaire is in an unknown network and needs to be unpaired and then paired again before it can be controlled from Luminaires tab
To pair the "Unpaired" luminaire please tap on it and you can see the option to add it to a network.
To unpair the "Paired" luminaire tap on it and select "Unpair device". The app will open an unpair screen. After tapping "Start" wait for the orange bar to appear and then turn OFF the power from your luminaire. After few seconds turn ON the power for the luminaire. This will unpair it from the network.
Please also see article about unpairing: http://support.casambi.com/support/solutions/articles/12000021620-unpairing