Here is the instructions for change the Office 2021 / 2019 / 2016 Pro Plus key:
1- Open any Office app, select the File menu and then select Account near the bottom of the menu.
2- Under Product Information, select the Change License button.
3- After changed your license key you will find your new Installation ID so you can submit your Installation ID from our Get Confirmation ID page:
Remember, sometimes servers are stuck so if you can’t get your Confirmation ID within 30 second please refresh the page and submit again.
If you’re not able to get your Confirmation ID from the system please send us a Ticket from HERE.
4- After you enter your Confirmation ID your activation will be completed successfully.