Problems with HASS.Agent

I’ve replaced my son’s computer with a new one, and stupidly gave the new computer the same name as the old one, then installed HASS.Agent.
MQTT is working fine, but the device isn’t discovered with HASS.Agent and I can’t send notifications to it, which is my main requirement. I’ve seen some information that HASS.Agent is currently a little broken, and won’t add new devices unless you remove the integration and re-add. This kind of works, but pulls all the previous HASS.Agent devices back in, including the original PC under the original device name, even when it’s not powered up.
It looks like reinstalling the HASS.Agent integration automatically pulls back old devices and entities, which is what I’m trying to prevent. Any ideas how I can remove the HASS.Agent devices / entities so they don’t reappear automatically? At this point I just want to start from a clean slate with this integration.

I’ve managed to get the new laptop / HASS .Agent working, but I’m still not really sure how… Lots of deleting of the integration and re-adding.
I’m still confused as everytime the integration gets added, all the old devices / entities are “discovered”, even if they are no longer on the network. This suggests to me that the integration isn’t discovering, but just showing devices / entities that are stale entries left over in the configuration.
I have one old device left which I’ve disabled, but will probably never be fully cleaned up.