There are multiple different Clack water softener scenarios where it can be very useful to force the system into a regeneration manually. It's very simple to do:
Press and hold the REGEN button for about 4 seconds. Release the button when you hear the motor engage:

Once the regeneration has been initiated, it will go through all of the programmed stages. At each stage, the controller will display the stage name in the top left region of the screen, and you'll see a countdown timer showing the length of current stage. When the process is completed, the display will not show a stage name and instead the screen will show the time of day.