How do I change the web app to run on a different port as port 8000

[geraldatphotobucket]

That port is too common and causes conflicts. I can't any documentation when running under snap how to change this (or all the information suggested does not work)

Like:
snap get gutenprint-printer-app
error: snap "gutenprint-printer-app" has no configuration

Until this is resolved/better documented, I have no choice than to disable what looks like a useful application from my system.