The easiest way without any extra MIDI controllers/devices (and more especially if you have an 88-key keyboard) is to bind note events/key presses in the MIDI control/routing window. You can set any aspect of the stop knobs or combination system to be a key press event. In fact, I believe the default MIDI mapping has several of these enabled to demonstrate the functionality (which leads to very interesting and unexpected results if you open you a full-range MIDI file of piano or orchestral musics that goes below the default OTQ keyboard). There might also be regular keyboard key bindings for select functions, but it's been a while since I experimented with much of that.
Pat's excellent StreamDeck stuff, the JSON Rest API serer, and additional MIDI hardware are other ways to do it as well (with varying degrees of technical knowledge and time investment to set up). Unfortunately, OTQ doesn't currently support MIDI out so some advance console functionality that depends on it won't work (you can't update an external MIDI device with an internal OTQ MIDI/Sys state change).
Spotify:
https://open.spotify.com/artist/2xHiPcCsm29R12HX4eXd4JPianoteq Studio & Organteq
Casio GP300 & Custom organ console