For Cavities to work as intended, two settings have to change in the admin. Go to "Client" -> "Administration" -> "System settings" -> "eTouch" -> "Define eTouch parameters" -> "eTouch parameters 2". Activate the tick box "Cavity control", and then enter the amount of cavities allowed in the menu for "Max cavities". Here there is more information on how that form works.

Once that is done, the form seen below will be available. Use the buttons to enter a number of cavities up to the limit entered in the "Max cavities" menu. Use save to confirm, and cancel to abort.