How to communicate programmatically from dmz(orange) to green

I have setup my Network with ipfire so that i have red, orange, green and blue zones.

The Green Network is reserved for a Server where I want to put on a Database and a Programm in form of a Rest API to Retrieve Data out of my Database.

Inside the DMZ I have another Server that acts as a WebServer that recieves Requests from an Application. To create the appropriate Responses I need some Data from my Database. How can I achieve this without exposing my green Network?

Allowing connection only from the server into DMZ to the ports you need on the server into green.