How to pair, please try following steps:
Step1: Keep your PC on, and be sure the keyboard is full of power.
Step2:Press the “F1” without releasing.
Step3:Power on the keyboard and release the "F1" immediately.
Step4:Plug the USB receiver on the USB port of your PC.
Wait a moment. The keyboard will r1epair automatically.
When the light stop flashing and green led on, it means successful.