Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
I am not sure that the users Microsoft Account will not have been used for over two years. It will depend on whether the OP used an online account or a local account so that his Office his Microsoft Account is consistently in use whenever he uses Office. I am not sure if is is the same with use of a local account, so that it is used to sign into Windows consistently. However, the OP is going to have to contact Microsoft Support in any event.