The Manual Tool Change Button needs a couple of things in order to work: 

First the safety/run wire must be connected between the VFD and Pneumatics Enclosure (PE). This will allow the button to light when in the spindle is in a stopped position. 

The safety/run wire is a GX12-2 Pin female to GX12-2 Pin female connector and goes into the "Run" port on the VFD, and "RUN" on the PE. The wire is necessary otherwise the PE would not know the state of the spindle and you would be able to activate the solenoids while the bit is spinning, so without the wire, the button will not be able to be enabled. 

Note: If the MTC is lit up, and the air supply is turned off, you should hear an audible click when pressing the MTC Button. This assumes your PE is on properly. 

To verify the PE is turned on, a visual indicator is upon inspecting the top, that there is a red-light glow. 

Finally, the VFD must not be in a run state, or the MTC Light will go out, rendering it unusable at that time. If your controller is able to activate the run state, the controller must not be putting it in that state. 

If neither of these allows the MTC Switch to be illuminated, verifying that P2.0.29 is set to"1" would be the next logical step. Instructions on how to do this can be found here in the flow chart.