It's easy to change the owner of a Cid number: first, go to the information view of the Cid number in question, i.e. the "Number Routings" tab.

In the "Number owner" drop-down menu, select a new owner for the number and click on "Save" to save the change.

If the Cid number does not have an owner, you can assign the Cid number to your preferred user, in which case the user will also become the owner of the number.