For each frequency range there are two caps and two resistors. Adjusting those will adjust the frequency. if you look at the schematic pot 6 c5, c6, r10 and r11 set the frequency.
I’m sure someone else will chime in with quality component recommendations.
So, let’s say I wanted to change the frequencies on some of the pots for the 6 band eq. What would be the formula if I wanted to use a freq that’s higher or lower?