Here is Geoff Duke's blog posting on activation problems. You could probably skip the troubleshooting parts and go right to the activation trigger, number 5 in the list.
CAS Computing Services
From: Technology Discussion at UVM [mailto:[log in to unmask]] On Behalf Of Lynda Howell
Sent: Wednesday, May 10, 2017 10:17 AM
To: [log in to unmask]
Subject: force PowerPoint reactivation?
Is there any way to force PowerPoint 2013 to reactivate?
We have a department-owned, CAMPUS-joined laptop that is not normally connected to the network, and Windows and Office needed to be reactivated periodically. I connected it to the network and was able to reactivate Windows, but I can't find a way to tell PowerPoint to reactivate. The only option it's giving me is to change the product key (but I don't have one to give it). It says it will reactivate automatically, but I'm too impatient to wait for it to get around to it. How can I force it to check in with the server for the automatic reactivation?