Edit the file /etc/netplan/50-cloud-init.yaml like the one below and just substitute the appropriate IP adddress, gateway and DNS servers for your environment.

network:
     ethernets:
         enp0s3:
             dhcp4: no
             addresses: [192.168.88.18/24]
             gateway4: 192.168.88.1
             nameservers:
                     addresses: [192.168.88.1,8.8.8.8]
     version: 2

then do:

$ sudo netplan apply