Oracle Forms

dear all

i using form6i and run in c\s

i need to know how to make that if a person reserved a room for 3 days and if expired it will automatically back the quantity of the available rooms.

here is the example
i have 5 available rooms , mica booked for 1 room then room available will become 4. mica book the room for 3 days if the date expired the available rooms will back to 5 available automatically.

can any one help me to do this... i getting mad to my school....