I recommend reading the manual.
Press the bind button on the RX and turn it on. Make a new model ID on your tx, set it to FrSky D8, and press bind.
The lights on the RX should change. Turn off rx and tx and restart. Light on rx should be green.
If this doesn't work adjust freq_fine / Freq_coarse by +30 and - 30 until you get a bind.
Good luck