Modify the Port to new port number (i.e: 23)

Port 23

Restart ssh service

/etc/init.d/ssh restart

If not working, modify file below;

vim /etc/systemd/system/sockets.target.wants/ssh.socket

Modify the "ListenStream" value to target (i.e: 23)

Restart systemctl daemon & ssh service

systemctl daemon-reload
/etc/init.d/ssh restart

Ref: https://askubuntu.com/questions/1483893/unable-to-change-ssh-port-on-ubuntu