Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
There is no option to merge two Microsoft accounts. You can migrate data from the one you want to retire to the one you want to continue using. Make sure that one you want to keep using is the one connected to your Microsoft 365 subscription. You can't transfer subscription from one Microsoft account to another. You can check it here: https://account.microsoft.com/services While you are on this page, you can find "Install desktop versions" and use it to install Office onto new PC.
Do not close Microsoft account before you created a backup and/or migrated all data (email, documents, ...).