Lotus notes coding a button that produces a pop-up prompt with a drop down.

I have an existing Lotus notes database form that I am trying to create a button that will help  a certain set of users can click to rapidly fill in some fields. The long story short is that we are not modifying the app itself, rather coding/adding an external button to the users tool bar in notes to do this.

All I am looking to do is with the form the open and in edit mode, is have the user execute the button. Upon clicking it they will get a prompt to select a value from a drop down and click ok, this selected value will then populate a field on the form....once that value is selected several @setfields command execute and populate the form.  I have the setfields commands all working, I am having issues coding the prompt and drop down list (I'm relatively new to notes coding).  I am attempting to use the @prompt() function which at least gets me the pop up, but I am uncertain how to code the drop down list in it.