To make a claim active again you can do one of the following:
From Claims page, search for the patient or claim, and tick the red X in the ACTIVE column, this will change it to a tick and the claim will be active.
From the patient's page, in the Claims list section tick the red X in the ACTIVE column, this will change it to a tick and the claim will be active
Edit the claim and tick the Active tick box, then Save.