In our case we "Cancel" the newest one (or the one that got less information if there is the case), and as the system ask for a reason, we refer to the one that stays open: "Cancelling Incident as duplicated, see Incident #100001"
Also we added the option to link Incidents to Incidents, so we would link both Incidents, but that is not that necessary.
That is our approach, but you should think what works for you, do you keep track of the time spent? maybe ask about the time when cancelling so the time spent for that analyst does not get lost, maybe "Resolve" the Incident, but add something like the previous message as resolution.
Hope this helps!