You can’t. Marlin runs on the Arduino and controls the timing of the motors (over simplified explanation). In a Mach 3 system, the windows computer has the same role that the Arduino does, and the computer controls the motors directly. The controller is the computer itself.
They basically fulfill the same role, therefore, they cannot be used together. If you want to run grbl, bCNC is really close to the functionality/wizards thatach 3 has.