How to remotely remove an insightvm agent?

We installed the insightvm agent on a contractor’s machine (macos) and had it reporting risks to the server.
After the contractor left, they did not uninstall the agent, so we still get it appearing in our reports (but with ever-growing risks from being unpatched …). I am not able to contact the machine owner to get them to remove the agent.

I can delete the asset in InsightVM, but it just repopulates within a couple of days. I cannot remove it from the Agents screen at all.

How can I remove/blacklist this from the Agents so that it never repopulates itself, or remotely uninstall/disable it on the remote workstation (though as this is a personal machine making remote changes after contract end is likely not legal)?