Fill Slot which is not part of a form based on if a particular slot is filled

Hi, So I’m trying to fill a slot using custom action/validation when a particular slot in a form gets filled up… i.e fill slot_2 automatically with the computed zip code gotten from address if slot_1 has been filled up with the address. I cannot add slot_2 to the form because I do not need a ask_slot response that slot. I tried using requested_slot: slot_1 when defining slot_2 but it doesn’t work. Please how do I go about it?

You can define your own required_slots method as described here.