DBT - 06103 The port (1521) is already in use

When creating a new Oracle (db19c) - for step7 - create listener - I am getting error DBT - 06103 The port (1521) is already in use

Trying to find a solution.

It gives me the listener status on that server but it does not show on the screen of dbca as existing listener - this is why I was trying to create a new one but getting the error 'port in use'

Should I have listener.ora and tnsnames.ora files on that server before creating instances on that server. Is that the problem?

Need some quick help here.