How to point react/npm/node.js UI to non-node.js web service

I'm working on developing a front end using ReactJS. I'm new to node.js, react, and web dev. I've created a dev environment using the create-react-app capability. I can edit my js/jsx and it gets immediately reflected in the browser but I'd like to be able to point it to a service not hosted from node. I have an existing service written with Spring Boot that I need to put a frontend on. How can I get my project to connect to that service?