A family of Microsoft word processing software products for creating web, email, and print documents.
Have you already updated your Mac to Sequoia 15.8? If so, use the Office License Removal Tool to remove the existing Office license from your Mac: https://support.microsoft.com/en-us/office/how-to-remove-office-license-files-on-a-mac-b032c0f6-a431-4dad-83a9-6b727c03b193 and run the license removal tool.
Then sign in to your Microsoft account that has Office Home and Student 2021 at https://m365.cloud.microsoft/apps. Click Install apps in the top right, then open Word and sign in with the same account to activate Office.