If you click the + at the bottom, it should let you use another. Main thing is that one of the 8.8* ones is the top one, so if there's any existing one there, you can drag it to the bottom of the list, like this.
The IP address 198.168.1.nnn is a local IP address inside your router. Unless you are running your own DNS, then this is an invalid DNS. Domain Name Servers are just that, servers that are dedicated to translating Domain Names to a valid IP address. It is a lot easier to remember the name than the 12 digit number that is used to route traffic across the internet. Your router usually has an internal IP address of 192.168.1.254 and an external IP address assigned by your ISP. The ISP send traffic to your router which then routes the packet destination to defined as one of the devices inside your LAN.