How to add an address to DNS
Solution 1:
The easiest way is to go to
Settings -> Network -> LAN Interface (Cog Symbol) -> IPv4 Settings (tab) -> Additional DNS Servers
If you must do it from the command line, then you can type:
sudo nmcli con mod enp0s31f6 +ipv4.dns "172.26.5.14"
update with:
sudo nmcli con up "enp0s31f6"