How to keep private my app using Kubernetes

I’m new on Kubernetes world and I launch a new EKS cluster with Gitlab integration and I’ve already deployed an express app from Gitlab’s template. But I have a big question. Can I keep private my applications?

I’ll use this Kubernetes cluster to deploy some critical services for our organization, but I want keep them privates and only accessible via AWS API Gateway for example. This is possible? What would be the best way to do it?

Thank you so much for your help.
Best regards