Lost access to HA, OK via HA Cloud on mobile

I’ve just lost access to my HA machine, which is on a little Dell Optiplex PC.
My phone can assess it using HA Cloud, but my PC in the same house cannot access it. It just comes up with a time out.
Recently had a change of ISP and router and I’m going to assume that this is the reason.
HA cannot have the same static IP as it used to have as the linksys router is using 192.168.1.x range, the TPLink old router was 192.168.0.x
I know the box is on line as it’s in the list of devices and I can ping it ok.
I have physical access to the HA box and can plug a screen / keyboard into it.

It was originally set up with a DuckDNS address which worked in and out of the house.

DuckDNS is showing the new IP address for the connection.

I can’t get it to react to homeassistant.local:8123
I did recreate the port forwarding that was on the old router (obviously with the new IP address)

As I now subscribe to HA Cloud I am guessing that this might be resolved by resetting the network config to default ?

All help much appreciated.