To find out what product keys we have associated with our Microsoft account we must visit this link:
This is where we have to log into our Microsoft account. Once we have logged in we will visit this other link:
It is important to note that for the last link to work by showing us the associated product keys, we must have logged into our account.
Here we see how the product keys associated with the Microsoft account show us. They also give us the option to download a copy of Office, which is activated with the product key shown.
For each key there is a different download. To activate the downloaded Office installation it is absolutely necessary to use the product key that gave us the download option.
Everything explained here would also serve to see the associated Office 2019 product keys