When a Microsoft 365 licence is activated, that licence is permanently linked to the Microsoft account as a digital licence and there is no method provided to move the licence to another account, on the link below, Microsoft provides the information about moving an Office licence to another account, if you are living in the EU, they provide the steps to do this
Either way, you would need to contact Microsoft Support directly, provide them with proof of purchase and ask them if that licence can be moved to the other account, try using this method to contact their support.
Go to this link: https://support.microsoft.com/contactus
Select Microsoft 365
Click 'Get Home Support'.
In the box provided, type billing.
Press Enter, then on the next page, scroll down and click 'Sign in to Contact Support'.
Navigate to Microsoft 365 and Office - Manage my Subscription.
Select the 'Chat with support agent in web browser' option