Commands step by step

edit setting file sudo nano /etc/netplan/50-cloud-init.yaml

network:
  ethernets:
    enp0s3:
      addresses: [192.168.1.10/24]
      gateway4: 192.168.1.1
      dhcp4: no
  version: 2

note you should change the ip 192.168.1.10 to the static ip value you want to apply.

apply change sudo netplan apply

restart machine sudo shutdown -r now

Done.