HELLO JYOTI RAINA..
Well if you are talking about plotting BER and Q-factor against two quantities which are power and fiber distance at the same time then it is not possible for now in optisystem graphs..This problem of not being able to plot various parameters for more than one transmitters or receivers has been mentioned quite often.. Now what you can do is use the excel option for plotting such graphs.. I hope it helps you to some extent.
Thanks & regards