Load Existing Options can be used when you have created a form using an existing layer. 

1. Click "+NEW" from the forms menu. 
2. Find your data under "LAYERS WITHOUT AN EXISTING FORM", and click "CHOOSE".
   
3. Fill out the NAME and DESCRIPTION (Optional).
   
4. Click "SAVE".
   
5. The layer's existing fields will be translated into questions in your form.
   
6. Hover over the field name that you want to edit and click the pencil icon.
   
7. In the "WIDGET" drop down, click "Select from List".
   
8. Click "SETUP PICK LIST".
   
9. Click the 3 horizontal dots "..." on the top-right of the box. 
   
10. Click "Load Existing Options".
    
11. This will extract and create a pick-list of all the unique values currently stored in that particular field. For future form submissions, users will be able to select from the pick-list that was just loaded.