How to utter_ask_<slot_name> again when the entity extracted failed and slot was not filled?

thank u for your reply. In this topic how-to-deactivate-a-form-during-validation , a professor said “Your validate action can return ActiveLoop(None) event to deactivate the form.”, but it seems that validate_<slotname> function can just return a dic which includes the slot name and value.

May I ask how can I deactivate the form in my validate_<slotname> function? Thank you.