After having been in beta since a while and being used at CERN without issues, we just released a stable version of the Zoom plugin for Indico.
Documentation on how to install plugins can be found here: Plugins — Indico 2.3.4 documentation
If you already have the indico-plugins bundle installed, just update it; otherwise you can pip install indico-plugin-vc-zoom to install just the Zoom plugin.