Tvheadend calls what you watch on your TV a "channel". What your input sources provide it calls a "service". Linking a channel to a service is called "mapping".
Though it complicates setting up, this distinction between services and channels is really useful. If you have two or more services providing the same TV channel, then mapping both to the same tvheadend channel provides redundancy against failure and (if you have multiple input sources) allows tvheadend to use an alternative source if the first is busy.
I don't believe there is an "unmap" option available, the simplest solution is to delete all of your channels and start again with the mapping process.
