The solution below is designed to help customer with uninstalling Office 365 from Mac device and remove any previous stored Office 365 licenses. Common problem with editing word files on Mac OS device is because the customer hasn't either signed in with University email address, or the customer is using a trial version of Office 365.

Before installing Office 365 on Mac device, the customer should be advised to uninstall any other version of MS Office. 

The following link helps with uninstalling Office from Mac

https://support.office.com/en-ie/article/uninstall-office-for-mac-eefa1199-5b58-43af-8a3d-b73dc1a8cae3

The following link will help with removing any previous stored Office 365 licenses

https://support.office.com/en-us/article/how-to-remove-office-license-files-on-a-mac-b032c0f6-a431-4dad-83a9-6b727c03b193

Once the steps above are completed, the customer can restart the device and install Office 365 from beginning.