setting up for Slack App dropdown menu

Hi , I am trying to setup a dropdown option in my slack app. where If a user selects a text , I want to simply return the value associated to that text,

How I write my Entity User Prompt - particular to slack app where a dropdown is created and backend value for the text selected is displayed???

In my dropdown menu I have names of countries such as US, India, UK, Japan, China etc.
and the value associated in the backend are currency names such as Dollar, Rupee, etc.

Thanks & regards
Surya