You can refer to the step-by-step guide or the video below:
Turn off the power to the receiver as well as transmitters B & C before you get started.
Power on transmitter B and reset it by clicking the top button 10 times. A flashing 605.000 channel number shows up if you reset transmitter B properly.
The same goes for transmitter C. But what appears on the transmitter is the flashing 584.000 channel.
When they are still flashing, switch on the receiver. Pay a bit of attention here if its RF B & C lights will blink 3 times before the last step.
Click the top buttons of both transmitters B & C, resulting in pairing successfully.