Populate dropdown based on other dropdowns

I am builiding an app to book a nurse based on the schediuled they provide. Here are my key collections

  1. Calendar (has a relationship with nurse (M:M) and a relationship with slots (M:M))
  2. Slots (just a collection of 30min time intervals)
  3. Nurse

I would like to 1) pick a date 2) pick a nurse and 3) have all slots available for that day and that nurse as options on a dropdown

I am able to retrieve the data through a nested list - however, I have no idea how to pull the data into my dropdown. Please see image below. Instead my entire drop down is populated by all my slots but not the ones available for that day and nurse. Please help !!