The EQ sounds like it is broken up into Low , Middle and High

For each EQ range there are 2 knobs.
One knob is frequency
One knob is boost\cut
So you pick a frequency and either boost it a couple decibles or cut it a couple decibals. Boosting the high frequencies is not quite the same as cutting the low frequency.
For voice I think you generally want to boost the frequency around 1 Khz a couple of decibals and cut the lower frquencies to get rid of some of the breathy sound. I'm sure there are plenty of people here who can recommend much better EQ settings than I can, but maybe this will be a helpful summary of the ppurposes of the knobs.