https://community.spiceworks.com/how_to/48973-remove-and-re-add-license-key-for-office-2013-on-office-365

Open a Command Prompt window, and then take one of the following actions:

• If you installed the 64-bit version of Office 2013, move to the following folder: C:\Program Files\Microsoft Office\Office15
• If you installed the 32-bit version of Office 2013, move to the following folder: C:\Program Files (x86)\Microsoft Office\Office15

cscript ospp.vbs /dstatus

cscript ospp.vbs /unpkey:<last five characters of product key>

Restart