If your problem is the Z axis Home position not at Z axis arrow mark position
Please use MPG to move the Z axis (Ram) the let Ram Z0 arrow to match with Ram base Z0 arrow then execute Z axis Home position reset procedure as attached file (from pdf page 7~) And follow below video instruction.
Video “How to reset Z axis Home zero position procedure”:
If your problem is about how to set start slotting point and bottom slotting point in dialogue Program edit , Please refer the video here .
Video : How to set start slotting point & bottom slotting point in dialog CNC-450