I am sorry. I never play with this equalizer, so I did now for you.
You are right, that panel is scrollable and there is a hidden low frequency 250Hz. But no higher than 8kHz.
But on the bottom of the screen there are two boosters for Bass and T...
As you clearly see from that screenshot it is a 500Hz, so it is not good enough for you.
There's a single "z" at the bottom left of the eq, might be scrollable. Also I find it hard to believe 8khz is the highest