By default the Oracle SQLNet Listener is updated once a minute with newly started instances, PMON does this.
If you don’t want to wait the one minute, do this:
Logged into the instance as sysdba “sqlplus / as sysdba” issue this alter system command:
SQL> alter system register;
Your instance will be immediately registered with the listener.
lsnrctl status LISTENER_NAME — if different than default name – LISTENER