How Do I Use Port Forwarding on a Lan/wan-Attack

Hey i was wondering how to use port forwarding on this wan-attack This video is the attack i am doingMy router has port-forwarding and the model is cisco dpc3827.My computer has kali linux installed on it.I have already succesfully done this attack on someone on my own network and it was succesful.I was also wondering how to possibly inngect this into like a game or other app but i do not know anything about port-forwarding or like the ports to pick or how to set it up.If you need any extra info i will be glad to provide it.