Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
You purchased the MS Office license 15 years ago from Dell. Did it come pre-installed on a computer which you purchased from Dell? Do you still have the computer? Can you find license information on it? Do you have a receipt or any other document from Dell showing the purchase or license information? Have you asked Dell if they have a record of the license? Without some documentation it's going to be very hard to track down anything useful.
You mention a "previous office". Is that an office where you work? Or do you mean a previous version of Microsoft Office? Same circumstances. If you have documentation such as a receipt identifying the license or licenses you purchased, or the name under which you registered the licenses, it's difficult to think of a way to retrieve information about it.
In any event, this forum support the MS Access database application and it's not staffed by Microsoft support personnel.
I suggest you start here: https://support.microsoft.com/en-us/support/