product key

1

If you have purchased a Microsoft 365 subscription from a 3rd party retailer, this is a first-time activation and have a keycode card, if you have not activated that licence yet, log into this link and enter the product key to link Office to your Microsoft account.

https://setup.office.com/Home?wa=wsignin1.0

2

If you have previously activated the Microsoft 365 Personal subscription and need to re-install it, when you first activated Office that licence should have become associated to your Microsoft Account as a digital licence online and it is from there that you can re-install Office without the need for a product key:

https://account.microsoft.com/services/