GitLab Auto DevOps - how to point to the custom docker registry?

Hello, I am hosting a GitLab instance (without Container Registry), but I am hosting also a Nexus 3 based Docker Registry. I would like to use this registry, instead of built in from GitLab - however I don’t see any env variables which could overwrite these settings… Any hint where to look or if it is even doable at all?

Cheers,

Rafał