How can I configure where the NPM packages will be read

We using a local NPM regisrtry(sinopia) that holds our local developed tools. I like to use now this "local" NPM registry instead of the official one as.

If I open the screen for node to show all configured NPMS (reading the package.json file) then I can trace that the request is made correct to the local NPM registry.
But I like to add a new package in the UI I can't see any trafic going out. Where webstorm is reading the list and how can I clear this cache?

Thanks Dirk