Wow just found this myself if anyone else is looking to do this.
This data is stored on the Category object. Just replace the category # with your category:
db.objects.find( { _key : "category:#"} ) .pretty();Next you can use the update() method to change the values to match.
db.objects.update( { _key : "category:#" }, { $set : { "topic_count" : numberofTopics } } );