Couple of questions.
1. Is the eircom modem a router/modem combo device? If its a combo device, either the orbi needs to be in Acces Point mode or you need to put your eircom in bridged/modem only mode if you want the Orbi in router mode. In AP mode the Orbi won't show as being online but everything will work.
2. On the back of the Orbi, are you connected to the standard LAN port or the WAN port?
Just trying to get this straight on what you're trying to accomplish and the best way to do so.
here's some info on setting Orbi in AP mode.
Its best to talk to your provider on how best to switch your eircom if you're switching the modes on that.
From looking it up, it is a combo device. Here's you options.
1. Leave it as is and put Orbi in AP mode. You can disable wifi on the Eir device so it doesn't create interference. This is probably the simplest route for you. Orbi won't show as online in the orbi menu but it will work fine. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point
2. Setup the Eircom as modem/dsl/bridge mode only. Check with your provider on how to do this properly for this device. I'd rather not mess it up for you This would allow you to use the orbi in router mode and use its features.
Up to you which route you choose.
Thank you for all your help. I couldn’t have done it without you!