It's also done when guys first get in the jet, as part of the contact phase of their training. This is when you learn how the aircraft flies...you perform maneuvers that expose you to the entire flight envelope from traffic pattern stalls, to single-engine airwork, to maneuvering without SAS and in MRFCS.
To get into MRFCS, you should establish level flight above 10,000ft, and between 180-210kt with the aircraft trimmed for level flight.
Move the mode switch to MANUAL REVERSION and note that the left and right hydraulic gauges are less than 250psi.
At that point, the L and R HYD PRESS caution lights, and the L and R AIL TAB caution lights should be illuminated with a flashing Master Caution.
The ailerons will float up, the slats will extend, and the airplane will be in manual reversion.
Stick forces can be very high, and improper use of power, trim, and or airspeed can cause stick forces that cannot be overcome.
To return to normal control, perform the same procedure in reverse.