Err need more info...assuming that there are no other switches on there, you must be able to choose full frequency, low pass or high pass output. The 70/100 switch will give you high or low pass at 70 or 100hz. If youre low passing to the 6x9s you want to put it at 100hz. If youre high passing to the 6x9s then make it 70 so you get the widest range possible out of them and it just protects them from the lowest frequencies.
If youre running a sub then you want it low passed at 70..