EQ in note editor?

You can do that easily in Pro with the Spectrum Profile Note Edit.

in the pro note by note edit area, spectrum profile is one of 30 settings you can apply specifically to a note.
Everything happens (from an end user point of view of Pianoteq) as if each note had its own equalizer, however this "kind" of equalizer has for a given note, adjustments fixed on each of the frequencies of the partials of the note (frequencies also chosen according to the characteristics of each of the sets of strings in the note, 135 settings for the lowest notes, gradually reduced to 4 for the highest)
Besides that, there is also as in the standard version a global "equalizer". In fact these equalizers seem to act upstream for the construction of the sound, and not like conventional equalizers (like eq3 in the pianoteq effects for filtering downstream of the created sound)
To have the equivalent of a traditional equalizer on a set of notes, as if you were performing a keyboard split, it is also possible to use multiple instances of Pianoteq from a Daw simultaneously (standard as pro) by performing at the daw level the choice of keyboard split and applying a specific equalization for each of the Pianoteq instances. The problem is in this case a significant consumption of resources on the computer, contrary to what we have with the specific equalization note by note of Pianoteq pro, but with a behavior a little different.

Bruno

There are several ways to do what you're asking.  A few are in Standard and the rest in Pro.  It all depends on what particular aspect of the sound you want to reduce.  It's likely easiest on a question like this to try to figure out what would cause this problem in an acoustic piano and how a technician would fix it, and then emulated that change through the most related PTQ setting.

If you want to decrease the entire volume of each note (hammer attack, resonance, etc.), then use the Volume Note Edit in Standard.  Right click the Volume Slider and select Note Edit.  Decrease the volume of each bass note in the first two octaves by -3db to -6db or so (which will take away 50% to 75% of the sound).  Increase or decrease the volume of only those note any further, if needed.  The Note Edit for Volume or Tuning is the same window that you have in Pro, but we can load any UI feature into the Note Edit in Pro, as opposed to only those two in Standard.  The Spectrum Profile Note Edit is an overtone eq (rather like a stepped harmonic eq) where you can click on each note or note group and change the overtone eq.

Along the lines of what Bruno said, if you want to decrease the bass response of the entire instrument while keeping the same volume of the high overtones of the bass notes, use the EQ tool in Standard.  Add a control point somewhere between 110Hz and 130Hz and set it to 0db and then put another point at the left of the EQ graph at -6db, if you don't like the smoothing (e.g. the higher bass notes are louder), add another point around 100Hz and set it to -6db too.  I'm not aware of any differences in the graph EQ or FX EQ between Standard and Pro.  You can do something similar with the Parametric FX EQ3 tool, but you'll have few control points than you can add in the graphic EQ window, so I tend to only need the graph window which frees an FX slot anyway but then I don't usually many onboard FX and save adding during post in a DAW.

You can do the same thing at the same Hz frequencies with the resonance eq (if you want the notes to have the same attack volume they have now but fade to a quieter sound more quickly) and with the Resonance Duration EQ (if you want the notes to have the same attack but die more quickly) in Standard.

In Pro, the Spectrum Profile Editor allows you to apply a different volume to every overtone of each note, which is used to edit the voice/color/character of a note, since so much of what we hear in a piano's sound is related to the overtones (or partials) and soundboard resonance--not just the actual string vibration.  Pro gives you per-note control of the Dynamics Slider, so you could decrease or increase the difference between pp and ff for only the bass notes.  Per-note control of the Sympathetic Resonance (which is the volume of adjacent open strings along the harmonic series) which is another character or style of volume control.  Hammer hardness can be changed on a per-note basis, which will decrease the attack but keep the resonance relatively unchanged.

It's possible that you just need to use the Volume Note Edit in Standard, but the other options will give you different flavors of volume control for the bass notes.