How to configure config.js inside k8s - the default is wrong!

i am working on a helm chart. its starting up but I found connection error in the browser JS log.
the problem is that the web host is serving a config.js with a wrong xmpp configuration

config.websocket = ‘wss://localhost:8443/xmpp-websocket’;

the localhost:8433 is not from my config. How can I change it? the xmpp-socket is correctly configured on my web node at myhost/xmpp-websocket but where is this value taken from?

Do I have to create another docker image?

This topic hints at such a solution.
anyone has a pointer to the algorithm which creates the config.js?

Thanks for any pointers