How do I reference a related field in another application?

In "Application A" I have a form called "Customers" with fields name and email.

I am working in "Application B" where I have a lookup field that gets the ID from "Application A" - "Customers".

Question:

I want to get the email field from "Application A" - "Customers" while inside of "Application B" deluge script. How do I do this?