yup, the search function was the way to get hold of the entries. I didn't even need to change the reseller, but could use the delete function to have them erased from the bind9 configuration.
Funny enough: Even after I have deleted the entries that I found via search, it is still possible to find them... I have cross checked this: Even the oldest domain entries that have been deleted long ago can still be found through search. Bug or feature?!?!?