How do you subtract an imported HFSS 3D component from an already placed part?

I designed a probe and exported it using "Create 3D Component...". Then I placed the 3D component in a new design and it intersects with the waveguide I am trying to probe. When I try to subtract the probe from the waveguide solids the "Subtract" option is not available.

I am very new to HFSS so any help would be greatly appreciated.

Thanks,
Patrick