Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
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Uninstall any trial or subscription versions of Microsoft 365 currently on your computer to avoid license conflicts.
Open your browser and go to the Microsoft account services page.
https://account.microsoft.com/services
Sign in with the exact Microsoft account you used to buy Excel in 2021 > Look for Services & subscriptions or Purchased products to find Excel 2021 > Click Install next to Excel to download your specific license installer.