This will work for you.
go to
https://docs.microsoft.com/en-us/windows/deployment/upgrade/windows-10-edition-upgrades
where you will see a document. Scroll down until you see this text:
Then click the link circled as above.
You will get this page in the store. If you are re-installing Workstation on the SAME device it was on previously, MSFT says to click the buy link in order to re-activate the Workstations license after a re-installation or clean installation of Pro. If you are transferring to a new device you need to contact the Answer Desk by clicking the Get Help icon on your Start Menu and proceeding through the steps there.