You cannot reuse or edit a previous Campaign that either you (as an admin) or a previous admin has 'ended'. The purpose of ending a 'live' Campaign is so that the content is not recirculated amongst your employees - for a number of reasons deemed appropriate by the admin at the time of ending the Campaign.
This is also reflected in the Reporting per course/phish.
You can, however, copy the relevant Fusion template and rename it, to either update/recirculate it as part of a new Campaign.
You can also copy a phish template from its archive state and rename it to either update/recirculate as part of a new Campaign.