Lawgivers would enforce Landru's will by using what seemed to be an ordinary staff. They would aim it while under the control of the Landru computer, and the machine would take that opportunity to remotely strip the Betans from most of their free will, making them join "the Body" for the greater good of their civilization and live by the directives established by Landru.
In certain cases the absorption chamber would be used, as a single individual would be strapped to a wall as the procedure would be performed from a control room. It also appeared that some could resist the will of Landru, such as Tamar and Reger. (TOS episode & Star Trek 9 novelization: The Return of the Archons)