[?]: Reference point for Spindle with gearbox Sinumeric 840d

[BoozZzilla]

Can somebody help me with referencing of the spindle?
I need a manual, "how to".
Our artificers dissasembled a gearbox, motor was moved from it`s first position. And now i can`t set correct reference points.
I clearly understand how to reference cpindle without gearbox, but i can`t set this point`s at our machines - zeropoint always sliding out when i change gearbox step.
There is a 2-step gearbox. I`m trying to change 34090[0], 34090[1], 35012[1] and 35012[2] in axis machine data. How should i do it correctly?