Edit the config file and restart the network stack (NOTE: If you do this wrong, you may loose network connection - make sure you can get to the system physically or via your virtualization console if it goes wrong)
sudo nano /etc/netplan/01-netcfg.yaml
- Change address/gateway/nameservers as needed ctrl+O to save, ctrl+X to exit
Restart the network services (or reboot the host)
sudo systemctl restart systemd-networkd
Use yast to modify network settings. Make sure you tab through screens to set the netmask, gateway, and name servers too!