Initial configuration

I run a Fritz!Box Mesh network.  I have one device (a Humax YouView PVR) that I need to block access to a specific website to prevent automatic updates.  Although the Fritz!Box 7530 router boasts a Blocked Website feature, it is not a proper firewall and still allows network traffic to and from the router and the website.  So I bought a secondhand 110C thinking that I could insert it into the network between the Humax and my router.   Trouble is looking at Transparent mode, it looks as if the 110C needs the Management IP address to be x.x.x.1  but that is my routers' address.

I don't see that NAT mode is the right mode since the router provides NAT already.  But open to being told otherwise !

Any suggestions ?

TIA