Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Sorry to hear about this. The account originally used to install Office does not have to be the account used to activate it.
First, sign in to the following page with the account used for the renewal and confirm that Microsoft 365 appears as active:
https://account.microsoft.com/services
Then open Word and go to File > Account > Product Information > Switch License (or Update License) and sign in with the account that has the active subscription. Close and reopen all Office applications afterward.
Your documents will not be deleted by changing the activation account. However, files stored in OneDrive remain associated with the account where they were saved, so you may need to keep the former account listed under Connected Services to access them, as mentioned here: