Programming Z probes connected to expansion boards is not yet supported. For now you need to temporarily connect the Smart Effector to the main board if you want to change its sensitivity. I've logged this issue: https://github.com/Duet3D/RepRapFirmware/issues/815
dc42 created this issue in Duet3D/RepRapFirmware open Support programming Smart Effector sensitivity when the effector is connected to an expansion board #815