There is a process to sync collections from other GalaxyNG instances like the public galaxy. That’d be the best way to get it in.
Either way once it’s in you need to setup an execution environment with community.general installed into it (hopefully from your Private Automation Hub) or turn on the optional and legacy feature to install it on demand for every run containing that project. For a collection this is expressed in a file collections/requirements.yml.
Id recommend the EE approach as it is an install once behavior so jobs will run faster. It also pairs well with local development using ansible-navigator.