Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Use your account to download Office. Go to https://account.microsoft.com/services.
If you purchased Office 2019 recently from a third-party, make sure that you got a valid product key and associate it with an account via https://setup.office.com. Complete the installation using your account.
Note that some versions should be avoided. If you were offered Office Professional Plus, ask the retailer for the money back.